From f1a68455e0c81f8d3a9b8f170ca6077c2a4841f5 Mon Sep 17 00:00:00 2001
From: John Coffey <johnellis@linux.com>
Date: Sun, 16 Aug 2026 12:35:25 -0700
Subject: [PATCH] Build the ui/ component library and persistent app shell

Button, Input, Select, Badge, SeverityBadge, Table, Card, Modal,
Tooltip, Tabs, Skeleton, EmptyState -- a shared library so pages stop
hand-rolling markup per page (web/src/lib/components/ui, barrel export
in index.ts). Modal and CommandPalette are built on native <dialog>
for a real focus trap, Escape-to-close, and top-layer stacking instead
of hand-rolling those. Tabs uses roving tabindex with arrow-key nav.

NavSidebar replaces the old top-nav with a persistent sidebar
(Search/Dashboards/Alerts/Data Sources/Settings), a live tenant
indicator (api.ts's new getCurrentSession(), a client for the
already-existing POST /internal/authorize -- zero new backend surface),
theme/density quick-toggles, and a command-palette hint. Collapses to
an off-canvas drawer under 860px. CommandPalette (Cmd/Ctrl+K) indexes
the five static destinations plus live-fetched dashboards/alert rules.

Data Sources is a new, honestly-scoped placeholder page (one data
source per tenant today, no UI needed yet). Settings and Select-tenant
are re-tokened onto the new component library. +layout.svelte's content
wrapper is a plain <div>, not a second <main> -- every page already
renders its own top-level <main>.
---
 web/src/lib/api.ts                            |  30 +-
 web/src/lib/components/CommandPalette.svelte  | 222 +++++++++++++
 web/src/lib/components/NavSidebar.svelte      | 313 ++++++++++++++++++
 web/src/lib/components/ui/Badge.svelte        |  42 +++
 web/src/lib/components/ui/Button.svelte       | 106 ++++++
 web/src/lib/components/ui/Card.svelte         |  51 +++
 web/src/lib/components/ui/EmptyState.svelte   |  51 +++
 web/src/lib/components/ui/Input.svelte        |  57 ++++
 web/src/lib/components/ui/Modal.svelte        | 101 ++++++
 web/src/lib/components/ui/Select.svelte       |  60 ++++
 .../lib/components/ui/SeverityBadge.svelte    |  42 +++
 web/src/lib/components/ui/Skeleton.svelte     |  34 ++
 web/src/lib/components/ui/Table.svelte        |  52 +++
 web/src/lib/components/ui/Tabs.svelte         |  74 +++++
 web/src/lib/components/ui/Tooltip.svelte      |  46 +++
 web/src/lib/components/ui/index.ts            |  12 +
 web/src/routes/+layout.svelte                 |  80 +++--
 web/src/routes/data-sources/+page.svelte      |  54 +++
 web/src/routes/select-tenant/+page.svelte     |  36 +-
 web/src/routes/settings/+page.svelte          | 109 +++++-
 20 files changed, 1521 insertions(+), 51 deletions(-)
 create mode 100644 web/src/lib/components/CommandPalette.svelte
 create mode 100644 web/src/lib/components/NavSidebar.svelte
 create mode 100644 web/src/lib/components/ui/Badge.svelte
 create mode 100644 web/src/lib/components/ui/Button.svelte
 create mode 100644 web/src/lib/components/ui/Card.svelte
 create mode 100644 web/src/lib/components/ui/EmptyState.svelte
 create mode 100644 web/src/lib/components/ui/Input.svelte
 create mode 100644 web/src/lib/components/ui/Modal.svelte
 create mode 100644 web/src/lib/components/ui/Select.svelte
 create mode 100644 web/src/lib/components/ui/SeverityBadge.svelte
 create mode 100644 web/src/lib/components/ui/Skeleton.svelte
 create mode 100644 web/src/lib/components/ui/Table.svelte
 create mode 100644 web/src/lib/components/ui/Tabs.svelte
 create mode 100644 web/src/lib/components/ui/Tooltip.svelte
 create mode 100644 web/src/lib/components/ui/index.ts
 create mode 100644 web/src/routes/data-sources/+page.svelte

diff --git a/web/src/lib/api.ts b/web/src/lib/api.ts
index a3c1dfb..0916e38 100644
--- a/web/src/lib/api.ts
+++ b/web/src/lib/api.ts
@@ -16,7 +16,7 @@ export type Language = '' | 'sql' | 'spl';
 
 export type QueryResult = { columns: string[]; rows: unknown[][] };
 
-export type VizType = 'table' | 'line' | 'bar' | 'single_stat' | 'top_n';
+export type VizType = 'table' | 'line' | 'bar' | 'single_stat' | 'top_n' | 'heatmap';
 
 export type Panel = {
 	id: string;
@@ -203,6 +203,34 @@ export function selectTenant(tenantId: string): Promise<{ redirect_url: string }
 	});
 }
 
+export type CurrentSession = { tenant_id: string; user_id: string; role: string };
+
+// getCurrentSession backs the sidebar's tenant indicator (Phase 5).
+// POST /internal/authorize already exists (api/authz.HTTPAuthorizer and
+// alerting's queryclient call it the same way) and is already reachable
+// from the browser -- enterprise-auth's whole mux is wrapped in
+// WithCredentialedCORS, not just the tenant-picker routes -- so this is
+// a client for an existing endpoint, not a new one. Returns null for
+// every "no tenant to show" case alike (no enterprise-auth configured,
+// not logged in, or a plain single-tenant deployment) rather than
+// throwing -- same "absence is a normal deployment shape" posture
+// getAuthFeatures already uses, so the sidebar can just render nothing
+// instead of branching on error types.
+export async function getCurrentSession(): Promise<CurrentSession | null> {
+	if (!enterpriseAuthBase) return null;
+	try {
+		const res = await fetch(`${enterpriseAuthBase}/internal/authorize`, {
+			method: 'POST',
+			credentials: 'include'
+		});
+		if (!res.ok) return null;
+		const session = (await res.json()) as CurrentSession;
+		return session.tenant_id ? session : null;
+	} catch {
+		return null;
+	}
+}
+
 export function exportDashboard(id: string): Promise<Dashboard> {
 	return request(`/dashboards/${id}/export`);
 }
diff --git a/web/src/lib/components/CommandPalette.svelte b/web/src/lib/components/CommandPalette.svelte
new file mode 100644
index 0000000..d9dfc2b
--- /dev/null
+++ b/web/src/lib/components/CommandPalette.svelte
@@ -0,0 +1,222 @@
+<script lang="ts">
+	import { goto } from '$app/navigation';
+	import { listDashboards, listRules } from '$lib/api';
+
+	let { open = $bindable(false) }: { open?: boolean } = $props();
+
+	type Item = { id: string; label: string; hint: string; go: () => void };
+
+	const staticItems: Item[] = [
+		{ id: 'nav-search', label: 'Search', hint: 'Go to', go: () => goto('/') },
+		{ id: 'nav-dashboards', label: 'Dashboards', hint: 'Go to', go: () => goto('/dashboards') },
+		{ id: 'nav-alerts', label: 'Alerts', hint: 'Go to', go: () => goto('/alerts') },
+		{ id: 'nav-data-sources', label: 'Data Sources', hint: 'Go to', go: () => goto('/data-sources') },
+		{ id: 'nav-settings', label: 'Settings', hint: 'Go to', go: () => goto('/settings') }
+	];
+
+	let dynamicItems: Item[] = $state([]);
+	let loaded = false;
+	let query = $state('');
+	let selected = $state(0);
+	let inputEl: HTMLInputElement | undefined = $state();
+	let dialogEl: HTMLDialogElement | undefined = $state();
+
+	async function loadDynamic() {
+		if (loaded) return;
+		loaded = true;
+		const [dashboards, rules] = await Promise.allSettled([listDashboards(), listRules()]);
+		const items: Item[] = [];
+		if (dashboards.status === 'fulfilled') {
+			for (const d of dashboards.value) {
+				items.push({
+					id: `dash-${d.id}`,
+					label: d.name,
+					hint: 'Dashboard',
+					go: () => goto(`/dashboards/${d.id}`)
+				});
+			}
+		}
+		if (rules.status === 'fulfilled') {
+			for (const r of rules.value) {
+				items.push({
+					id: `rule-${r.id}`,
+					label: r.name,
+					hint: 'Alert rule',
+					go: () => goto(`/alerts/${r.id}`)
+				});
+			}
+		}
+		dynamicItems = items;
+	}
+
+	let allItems = $derived([...staticItems, ...dynamicItems]);
+	let filtered = $derived(
+		query.trim() === ''
+			? allItems
+			: allItems.filter((i) => i.label.toLowerCase().includes(query.trim().toLowerCase()))
+	);
+
+	$effect(() => {
+		selected = 0;
+	});
+
+	// Native <dialog> instead of a hand-rolled overlay -- same reasoning
+	// as ui/Modal.svelte: focus trap, Escape-to-close, and top-layer
+	// stacking come for free, and it resolves the a11y-linter warnings a
+	// plain role="dialog" div on a non-interactive element raises,
+	// rather than suppressing them.
+	$effect(() => {
+		if (!dialogEl) return;
+		if (open && !dialogEl.open) {
+			dialogEl.showModal();
+			loadDynamic();
+			queueMicrotask(() => inputEl?.focus());
+		}
+		if (!open && dialogEl.open) dialogEl.close();
+	});
+
+	function onDialogClose() {
+		open = false;
+		query = '';
+	}
+
+	function onBackdropClick(e: MouseEvent) {
+		if (e.target === dialogEl) open = false;
+	}
+
+	function choose(item: Item) {
+		item.go();
+		open = false;
+	}
+
+	function onKeydown(e: KeyboardEvent) {
+		if (e.key === 'ArrowDown') {
+			selected = Math.min(selected + 1, filtered.length - 1);
+			e.preventDefault();
+		} else if (e.key === 'ArrowUp') {
+			selected = Math.max(selected - 1, 0);
+			e.preventDefault();
+		} else if (e.key === 'Enter') {
+			if (filtered[selected]) choose(filtered[selected]);
+			e.preventDefault();
+		}
+	}
+
+	function onGlobalKeydown(e: KeyboardEvent) {
+		const isK = e.key === 'k' || e.key === 'K';
+		if (isK && (e.metaKey || e.ctrlKey)) {
+			e.preventDefault();
+			open = !open;
+		}
+	}
+</script>
+
+<svelte:window onkeydown={onGlobalKeydown} />
+
+<dialog bind:this={dialogEl} class="palette" onclose={onDialogClose} onclick={onBackdropClick} aria-label="Command palette">
+	<div class="frame">
+		<input
+			bind:this={inputEl}
+			bind:value={query}
+			onkeydown={onKeydown}
+			type="text"
+			placeholder="Jump to a dashboard, alert rule, or page…"
+			aria-label="Search"
+			role="combobox"
+			aria-expanded="true"
+			aria-controls="palette-listbox"
+		/>
+		<ul id="palette-listbox" role="listbox">
+			{#each filtered as item, i (item.id)}
+				<li role="option" aria-selected={i === selected}>
+					<button type="button" class:selected={i === selected} onclick={() => choose(item)}>
+						<span class="label">{item.label}</span>
+						<span class="hint">{item.hint}</span>
+					</button>
+				</li>
+			{:else}
+				<li class="empty">No matches</li>
+			{/each}
+		</ul>
+	</div>
+</dialog>
+
+<style>
+	.palette {
+		position: fixed;
+		top: 12vh;
+		left: 0;
+		right: 0;
+		margin: 0 auto;
+		padding: 0;
+		width: min(34rem, calc(100vw - 2rem));
+		background: var(--color-surface);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-lg);
+		box-shadow: var(--shadow-lg);
+		overflow: hidden;
+	}
+	.palette::backdrop {
+		background: rgba(0, 0, 0, 0.55);
+	}
+	.frame {
+		display: flex;
+		flex-direction: column;
+	}
+	input {
+		width: 100%;
+		height: 3rem;
+		padding: 0 var(--space-4);
+		border: none;
+		border-bottom: 1px solid var(--color-border);
+		background: transparent;
+		color: var(--color-text);
+		font-family: var(--font-ui);
+		font-size: var(--text-md);
+	}
+	input:focus {
+		outline: none;
+	}
+	input::placeholder {
+		color: var(--color-text-faint);
+	}
+	ul {
+		list-style: none;
+		margin: 0;
+		padding: var(--space-2);
+		max-height: 20rem;
+		overflow-y: auto;
+	}
+	li {
+		margin: 0;
+	}
+	li.empty {
+		padding: var(--space-3);
+		color: var(--color-text-muted);
+		font-size: var(--text-sm);
+	}
+	button {
+		width: 100%;
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		gap: var(--space-3);
+		background: none;
+		border: none;
+		border-radius: var(--radius-sm);
+		padding: var(--space-2) var(--space-3);
+		color: var(--color-text);
+		font-family: var(--font-ui);
+		font-size: var(--text-base);
+		text-align: left;
+		cursor: pointer;
+	}
+	button.selected {
+		background: var(--color-surface-raised);
+	}
+	.hint {
+		font-size: var(--text-xs);
+		color: var(--color-text-muted);
+		font-family: var(--font-mono);
+	}
+</style>
diff --git a/web/src/lib/components/NavSidebar.svelte b/web/src/lib/components/NavSidebar.svelte
new file mode 100644
index 0000000..693b88b
--- /dev/null
+++ b/web/src/lib/components/NavSidebar.svelte
@@ -0,0 +1,313 @@
+<script lang="ts">
+	import { page } from '$app/state';
+	import { getCurrentSession, enterpriseAuthBase, type CurrentSession } from '$lib/api';
+	import { getTheme, setTheme, type Theme } from '$lib/theme.svelte';
+	import { getDensity, toggleDensity } from '$lib/density.svelte';
+
+	let {
+		onOpenPalette,
+		mobileOpen = false,
+		onCloseMobile
+	}: { onOpenPalette: () => void; mobileOpen?: boolean; onCloseMobile?: () => void } = $props();
+
+	const navItems = [
+		{ href: '/', label: 'Search', icon: '◇' },
+		{ href: '/dashboards', label: 'Dashboards', icon: '▤' },
+		{ href: '/alerts', label: 'Alerts', icon: '▲' },
+		{ href: '/data-sources', label: 'Data Sources', icon: '◈' },
+		{ href: '/settings', label: 'Settings', icon: '⚙' }
+	];
+
+	function isActive(href: string): boolean {
+		if (href === '/') return page.url.pathname === '/';
+		return page.url.pathname.startsWith(href);
+	}
+
+	let session: CurrentSession | null = $state(null);
+	$effect(() => {
+		getCurrentSession().then((s) => (session = s));
+	});
+
+	const themeOptions: { value: Theme; label: string }[] = [
+		{ value: 'dark', label: 'Dark' },
+		{ value: 'light', label: 'Light' },
+		{ value: 'system', label: 'System' }
+	];
+</script>
+
+{#if mobileOpen}
+	<button type="button" class="backdrop" onclick={onCloseMobile} aria-label="Close menu"></button>
+{/if}
+
+<aside class="sidebar" class:mobile-open={mobileOpen}>
+	<div class="brand">
+		<span class="mark" aria-hidden="true">◆</span>
+		<span class="name">Sentry</span>
+		<button type="button" class="close-mobile" onclick={onCloseMobile} aria-label="Close menu">✕</button>
+	</div>
+
+	{#if enterpriseAuthBase}
+		<div class="tenant">
+			{#if session}
+				<div class="tenant-pill">
+					<span class="dot" aria-hidden="true"></span>
+					<span class="tenant-name">{session.tenant_id}</span>
+					<span class="role">{session.role}</span>
+				</div>
+				<a class="switch" href="{enterpriseAuthBase}/auth/oidc/login">Switch tenant</a>
+			{:else}
+				<a class="switch signin" href="{enterpriseAuthBase}/auth/oidc/login">Sign in</a>
+			{/if}
+		</div>
+	{/if}
+
+	<nav aria-label="Main">
+		{#each navItems as item (item.href)}
+			<a
+				href={item.href}
+				class:active={isActive(item.href)}
+				aria-current={isActive(item.href) ? 'page' : undefined}
+				onclick={onCloseMobile}
+			>
+				<span class="ic" aria-hidden="true">{item.icon}</span>
+				{item.label}
+			</a>
+		{/each}
+	</nav>
+
+	<div class="footer">
+		<button type="button" class="palette-hint" onclick={onOpenPalette}>
+			<span>Jump to…</span>
+			<kbd>⌘K</kbd>
+		</button>
+
+		<div class="controls">
+			<label for="theme-select" class="sr-only">Theme</label>
+			<select id="theme-select" value={getTheme()} onchange={(e) => setTheme(e.currentTarget.value as Theme)}>
+				{#each themeOptions as opt (opt.value)}
+					<option value={opt.value}>{opt.label}</option>
+				{/each}
+			</select>
+			<button type="button" class="density-toggle" onclick={toggleDensity} title="Toggle row density">
+				{getDensity() === 'compact' ? 'Compact' : 'Comfortable'}
+			</button>
+		</div>
+	</div>
+</aside>
+
+<style>
+	.sidebar {
+		background: var(--color-surface);
+		border-right: 1px solid var(--color-border);
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-5);
+		padding: var(--space-4) var(--space-3);
+		height: 100vh;
+		position: sticky;
+		top: 0;
+	}
+	.brand {
+		display: flex;
+		align-items: center;
+		gap: var(--space-2);
+		padding: 0 var(--space-2);
+	}
+	.mark {
+		color: var(--color-accent);
+	}
+	.name {
+		font-weight: var(--font-weight-bold);
+		font-size: var(--text-md);
+	}
+	.close-mobile {
+		display: none;
+		margin-left: auto;
+		background: none;
+		border: none;
+		color: var(--color-text-muted);
+		font-size: var(--text-md);
+		cursor: pointer;
+		padding: var(--space-1);
+	}
+	.backdrop {
+		display: none;
+	}
+
+	.tenant {
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-1);
+	}
+	.tenant-pill {
+		display: flex;
+		align-items: center;
+		gap: var(--space-2);
+		padding: var(--space-2) var(--space-3);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		font-size: var(--text-sm);
+	}
+	.dot {
+		width: 7px;
+		height: 7px;
+		border-radius: 50%;
+		background: var(--color-accent);
+		flex: none;
+	}
+	.tenant-name {
+		font-weight: var(--font-weight-medium);
+		overflow: hidden;
+		text-overflow: ellipsis;
+		white-space: nowrap;
+	}
+	.role {
+		margin-left: auto;
+		color: var(--color-text-muted);
+		font-size: var(--text-xs);
+		text-transform: uppercase;
+	}
+	.switch {
+		font-size: var(--text-xs);
+		color: var(--color-text-muted);
+		padding: 0 var(--space-3);
+		text-decoration: none;
+	}
+	.switch:hover {
+		color: var(--color-accent);
+	}
+	.switch.signin {
+		display: block;
+		padding: var(--space-2) var(--space-3);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		font-size: var(--text-sm);
+		color: var(--color-text);
+		text-align: center;
+	}
+
+	nav {
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-1);
+	}
+	nav a {
+		display: flex;
+		align-items: center;
+		gap: var(--space-3);
+		padding: var(--space-2) var(--space-3);
+		border-radius: var(--radius-sm);
+		color: var(--color-text-muted);
+		text-decoration: none;
+		font-size: var(--text-base);
+	}
+	nav a:hover {
+		background: var(--color-surface-raised);
+		color: var(--color-text);
+	}
+	nav a.active {
+		background: color-mix(in srgb, var(--color-accent) 14%, transparent);
+		color: var(--color-text);
+		font-weight: var(--font-weight-medium);
+	}
+	.ic {
+		width: 1rem;
+		text-align: center;
+		opacity: 0.85;
+	}
+
+	.footer {
+		margin-top: auto;
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-2);
+	}
+	.palette-hint {
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		width: 100%;
+		background: none;
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		padding: var(--space-2) var(--space-3);
+		color: var(--color-text-muted);
+		font-family: var(--font-ui);
+		font-size: var(--text-sm);
+		cursor: pointer;
+	}
+	.palette-hint:hover {
+		border-color: var(--color-border-strong);
+		color: var(--color-text);
+	}
+	kbd {
+		font-family: var(--font-mono);
+		background: var(--color-bg);
+		border: 1px solid var(--color-border);
+		border-radius: 3px;
+		padding: 0.05rem 0.3rem;
+		font-size: var(--text-xs);
+	}
+	.controls {
+		display: flex;
+		gap: var(--space-2);
+	}
+	.controls select,
+	.density-toggle {
+		flex: 1;
+		height: 1.9rem;
+		font-size: var(--text-xs);
+		background: var(--color-bg);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		color: var(--color-text-muted);
+		font-family: var(--font-ui);
+		cursor: pointer;
+	}
+	.sr-only {
+		position: absolute;
+		width: 1px;
+		height: 1px;
+		overflow: hidden;
+		clip: rect(0 0 0 0);
+	}
+
+	/* Below this width the sidebar becomes an off-canvas drawer
+	   (+layout.svelte renders a menu button to open it) instead of a
+	   fixed grid column -- "shouldn't break on a laptop screen or a
+	   tablet in landscape" is the actual bar (this is a desktop-first
+	   tool), so the breakpoint is deliberately narrower than a phone
+	   viewport would need. */
+	@media (max-width: 860px) {
+		.sidebar {
+			position: fixed;
+			left: 0;
+			top: 0;
+			z-index: 90;
+			width: 16rem;
+			transform: translateX(-100%);
+			transition: transform 0.15s ease;
+			box-shadow: var(--shadow-lg);
+		}
+		.sidebar.mobile-open {
+			transform: translateX(0);
+		}
+		.close-mobile {
+			display: block;
+		}
+		.backdrop {
+			display: block;
+			position: fixed;
+			inset: 0;
+			background: rgba(0, 0, 0, 0.5);
+			border: none;
+			z-index: 80;
+			padding: 0;
+		}
+	}
+	@media (prefers-reduced-motion: reduce) {
+		.sidebar {
+			transition: none;
+		}
+	}
+</style>
diff --git a/web/src/lib/components/ui/Badge.svelte b/web/src/lib/components/ui/Badge.svelte
new file mode 100644
index 0000000..41e72b6
--- /dev/null
+++ b/web/src/lib/components/ui/Badge.svelte
@@ -0,0 +1,42 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	// Generic status badge -- for severity specifically, use
+	// SeverityBadge.svelte instead (it owns the OTel->tier mapping so
+	// callers can't accidentally invent a sixth color).
+	type Tone = 'neutral' | 'success' | 'danger' | 'accent';
+
+	let { tone = 'neutral', children }: { tone?: Tone; children: Snippet } = $props();
+</script>
+
+<span class="badge {tone}">{@render children()}</span>
+
+<style>
+	.badge {
+		display: inline-flex;
+		align-items: center;
+		font-family: var(--font-ui);
+		font-size: var(--text-xs);
+		font-weight: var(--font-weight-bold);
+		letter-spacing: 0.02em;
+		padding: 0.1rem var(--space-2);
+		border-radius: var(--radius-sm);
+		width: fit-content;
+	}
+	.neutral {
+		color: var(--color-text-muted);
+		background: color-mix(in srgb, var(--color-text-muted) 16%, transparent);
+	}
+	.success {
+		color: var(--color-success);
+		background: color-mix(in srgb, var(--color-success) 16%, transparent);
+	}
+	.danger {
+		color: var(--color-danger);
+		background: color-mix(in srgb, var(--color-danger) 16%, transparent);
+	}
+	.accent {
+		color: var(--color-accent);
+		background: color-mix(in srgb, var(--color-accent) 16%, transparent);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Button.svelte b/web/src/lib/components/ui/Button.svelte
new file mode 100644
index 0000000..eb127fe
--- /dev/null
+++ b/web/src/lib/components/ui/Button.svelte
@@ -0,0 +1,106 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	type Variant = 'primary' | 'secondary' | 'ghost' | 'danger';
+	type Size = 'sm' | 'md';
+
+	let {
+		variant = 'secondary',
+		size = 'md',
+		type = 'button',
+		disabled = false,
+		href,
+		onclick,
+		children,
+		...rest
+	}: {
+		variant?: Variant;
+		size?: Size;
+		type?: 'button' | 'submit';
+		disabled?: boolean;
+		href?: string;
+		onclick?: (e: MouseEvent) => void;
+		children: Snippet;
+		[key: string]: unknown;
+	} = $props();
+</script>
+
+{#if href}
+	<a {href} class="btn {variant} {size}" aria-disabled={disabled} {...rest}>
+		{@render children()}
+	</a>
+{:else}
+	<button {type} class="btn {variant} {size}" {disabled} {onclick} {...rest}>
+		{@render children()}
+	</button>
+{/if}
+
+<style>
+	.btn {
+		display: inline-flex;
+		align-items: center;
+		justify-content: center;
+		gap: var(--space-2);
+		font-family: var(--font-ui);
+		font-weight: var(--font-weight-medium);
+		border-radius: var(--radius-sm);
+		border: 1px solid transparent;
+		cursor: pointer;
+		text-decoration: none;
+		white-space: nowrap;
+		transition:
+			background-color 0.1s ease,
+			border-color 0.1s ease;
+	}
+	.btn:disabled,
+	.btn[aria-disabled='true'] {
+		opacity: 0.5;
+		cursor: not-allowed;
+	}
+
+	.md {
+		height: var(--control-height);
+		padding: 0 var(--space-4);
+		font-size: var(--text-base);
+	}
+	.sm {
+		height: 1.75rem;
+		padding: 0 var(--space-3);
+		font-size: var(--text-sm);
+	}
+
+	.primary {
+		background: var(--color-accent);
+		color: var(--color-on-accent);
+	}
+	.primary:hover:not(:disabled) {
+		background: var(--color-accent-strong);
+	}
+
+	.secondary {
+		background: var(--color-surface-raised);
+		color: var(--color-text);
+		border-color: var(--color-border);
+	}
+	.secondary:hover:not(:disabled) {
+		border-color: var(--color-border-strong);
+	}
+
+	.ghost {
+		background: transparent;
+		color: var(--color-text-muted);
+	}
+	.ghost:hover:not(:disabled) {
+		background: var(--color-surface-raised);
+		color: var(--color-text);
+	}
+
+	.danger {
+		background: transparent;
+		color: var(--color-danger);
+		border-color: var(--color-danger);
+	}
+	.danger:hover:not(:disabled) {
+		background: color-mix(in srgb, var(--color-danger) 12%, transparent);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Card.svelte b/web/src/lib/components/ui/Card.svelte
new file mode 100644
index 0000000..c9999cb
--- /dev/null
+++ b/web/src/lib/components/ui/Card.svelte
@@ -0,0 +1,51 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	let {
+		title,
+		actions,
+		padded = true,
+		children
+	}: {
+		title?: string;
+		actions?: Snippet;
+		padded?: boolean;
+		children: Snippet;
+	} = $props();
+</script>
+
+<div class="card">
+	{#if title || actions}
+		<div class="head">
+			{#if title}<h2>{title}</h2>{/if}
+			{#if actions}<div class="actions">{@render actions()}</div>{/if}
+		</div>
+	{/if}
+	<div class="body" class:padded>
+		{@render children()}
+	</div>
+</div>
+
+<style>
+	.card {
+		background: var(--color-surface);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-md);
+		overflow: hidden;
+	}
+	.head {
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		gap: var(--space-3);
+		padding: var(--space-3) var(--panel-padding);
+		border-bottom: 1px solid var(--color-border);
+	}
+	.head h2 {
+		font-size: var(--text-base);
+		font-weight: var(--font-weight-medium);
+	}
+	.body.padded {
+		padding: var(--panel-padding);
+	}
+</style>
diff --git a/web/src/lib/components/ui/EmptyState.svelte b/web/src/lib/components/ui/EmptyState.svelte
new file mode 100644
index 0000000..1ee90c9
--- /dev/null
+++ b/web/src/lib/components/ui/EmptyState.svelte
@@ -0,0 +1,51 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	let {
+		icon = '◇',
+		title,
+		description,
+		action
+	}: {
+		icon?: string;
+		title: string;
+		description?: string;
+		action?: Snippet;
+	} = $props();
+</script>
+
+<div class="empty">
+	<div class="icon" aria-hidden="true">{icon}</div>
+	<h2>{title}</h2>
+	{#if description}<p>{description}</p>{/if}
+	{#if action}<div class="action">{@render action()}</div>{/if}
+</div>
+
+<style>
+	.empty {
+		display: flex;
+		flex-direction: column;
+		align-items: center;
+		text-align: center;
+		gap: var(--space-2);
+		padding: var(--space-8) var(--space-4);
+		color: var(--color-text-muted);
+	}
+	.icon {
+		font-size: var(--text-2xl);
+		color: var(--color-border-strong);
+		margin-bottom: var(--space-2);
+	}
+	h2 {
+		font-size: var(--text-md);
+		font-weight: var(--font-weight-medium);
+		color: var(--color-text);
+	}
+	p {
+		max-width: 30rem;
+		margin: 0;
+	}
+	.action {
+		margin-top: var(--space-2);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Input.svelte b/web/src/lib/components/ui/Input.svelte
new file mode 100644
index 0000000..1f5a29f
--- /dev/null
+++ b/web/src/lib/components/ui/Input.svelte
@@ -0,0 +1,57 @@
+<script lang="ts">
+	let {
+		value = $bindable(''),
+		type = 'text',
+		placeholder = '',
+		disabled = false,
+		id,
+		invalid = false,
+		...rest
+	}: {
+		value?: string;
+		type?: string;
+		placeholder?: string;
+		disabled?: boolean;
+		id?: string;
+		invalid?: boolean;
+		[key: string]: unknown;
+	} = $props();
+</script>
+
+<input
+	{id}
+	{type}
+	{placeholder}
+	{disabled}
+	bind:value
+	aria-invalid={invalid}
+	class="input"
+	class:invalid
+	{...rest}
+/>
+
+<style>
+	.input {
+		height: var(--control-height);
+		padding: 0 var(--space-3);
+		background: var(--color-surface);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		color: var(--color-text);
+		font-family: var(--font-ui);
+		font-size: var(--text-base);
+		width: 100%;
+	}
+	.input::placeholder {
+		color: var(--color-text-faint);
+	}
+	.input:hover:not(:disabled) {
+		border-color: var(--color-border-strong);
+	}
+	.input:disabled {
+		opacity: 0.5;
+	}
+	.input.invalid {
+		border-color: var(--color-danger);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Modal.svelte b/web/src/lib/components/ui/Modal.svelte
new file mode 100644
index 0000000..f552337
--- /dev/null
+++ b/web/src/lib/components/ui/Modal.svelte
@@ -0,0 +1,101 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	// Built on <dialog> deliberately -- native focus trap, Escape-to-close,
+	// and top-layer stacking for free, instead of hand-rolling all three.
+	let {
+		open = $bindable(false),
+		title,
+		children,
+		footer
+	}: {
+		open?: boolean;
+		title: string;
+		children: Snippet;
+		footer?: Snippet;
+	} = $props();
+
+	let dialogEl: HTMLDialogElement | undefined = $state();
+
+	$effect(() => {
+		if (!dialogEl) return;
+		if (open && !dialogEl.open) dialogEl.showModal();
+		if (!open && dialogEl.open) dialogEl.close();
+	});
+
+	function onClose() {
+		open = false;
+	}
+
+	function onBackdropClick(e: MouseEvent) {
+		if (e.target === dialogEl) open = false;
+	}
+</script>
+
+<dialog bind:this={dialogEl} onclose={onClose} onclick={onBackdropClick} aria-labelledby="modal-title">
+	<div class="frame">
+		<header>
+			<h2 id="modal-title">{title}</h2>
+			<button type="button" class="close" onclick={() => (open = false)} aria-label="Close">✕</button>
+		</header>
+		<div class="content">
+			{@render children()}
+		</div>
+		{#if footer}
+			<footer>{@render footer()}</footer>
+		{/if}
+	</div>
+</dialog>
+
+<style>
+	dialog {
+		padding: 0;
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-lg);
+		background: var(--color-surface);
+		color: var(--color-text);
+		box-shadow: var(--shadow-lg);
+		width: min(32rem, calc(100vw - 2rem));
+	}
+	dialog::backdrop {
+		background: rgba(0, 0, 0, 0.55);
+	}
+	.frame {
+		display: flex;
+		flex-direction: column;
+	}
+	header {
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		padding: var(--space-4);
+		border-bottom: 1px solid var(--color-border);
+	}
+	h2 {
+		font-size: var(--text-lg);
+		font-weight: var(--font-weight-medium);
+	}
+	.close {
+		background: none;
+		border: none;
+		color: var(--color-text-muted);
+		cursor: pointer;
+		font-size: var(--text-base);
+		line-height: 1;
+		padding: var(--space-1);
+	}
+	.close:hover {
+		color: var(--color-text);
+	}
+	.content {
+		padding: var(--space-4);
+		overflow-y: auto;
+	}
+	footer {
+		display: flex;
+		justify-content: flex-end;
+		gap: var(--space-2);
+		padding: var(--space-4);
+		border-top: 1px solid var(--color-border);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Select.svelte b/web/src/lib/components/ui/Select.svelte
new file mode 100644
index 0000000..440bbf9
--- /dev/null
+++ b/web/src/lib/components/ui/Select.svelte
@@ -0,0 +1,60 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	let {
+		value = $bindable(''),
+		disabled = false,
+		id,
+		children,
+		...rest
+	}: {
+		value?: string;
+		disabled?: boolean;
+		id?: string;
+		children: Snippet;
+		[key: string]: unknown;
+	} = $props();
+</script>
+
+<div class="wrap">
+	<select {id} {disabled} bind:value class="select" {...rest}>
+		{@render children()}
+	</select>
+	<span class="chev" aria-hidden="true">⌄</span>
+</div>
+
+<style>
+	.wrap {
+		position: relative;
+		display: inline-block;
+	}
+	.select {
+		appearance: none;
+		height: var(--control-height);
+		padding: 0 var(--space-6) 0 var(--space-3);
+		background: var(--color-surface);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-sm);
+		color: var(--color-text);
+		font-family: var(--font-ui);
+		font-size: var(--text-base);
+		width: 100%;
+		cursor: pointer;
+	}
+	.select:hover:not(:disabled) {
+		border-color: var(--color-border-strong);
+	}
+	.select:disabled {
+		opacity: 0.5;
+		cursor: not-allowed;
+	}
+	.chev {
+		position: absolute;
+		right: var(--space-3);
+		top: 50%;
+		transform: translateY(-50%);
+		color: var(--color-text-muted);
+		pointer-events: none;
+		font-size: var(--text-sm);
+	}
+</style>
diff --git a/web/src/lib/components/ui/SeverityBadge.svelte b/web/src/lib/components/ui/SeverityBadge.svelte
new file mode 100644
index 0000000..8610d83
--- /dev/null
+++ b/web/src/lib/components/ui/SeverityBadge.svelte
@@ -0,0 +1,42 @@
+<script lang="ts">
+	import { severityTier } from '$lib/severity';
+
+	let { severity }: { severity: string } = $props();
+	let tier = $derived(severityTier(severity));
+</script>
+
+<span class="chip {tier}">{severity}</span>
+
+<style>
+	.chip {
+		display: inline-flex;
+		align-items: center;
+		font-family: var(--font-mono);
+		font-size: var(--text-xs);
+		font-weight: var(--font-weight-bold);
+		letter-spacing: 0.02em;
+		padding: 0.05rem var(--space-2);
+		border-radius: var(--radius-sm);
+		width: fit-content;
+	}
+	.quiet {
+		color: var(--color-sev-quiet);
+		background: var(--color-sev-quiet-bg);
+	}
+	.info {
+		color: var(--color-sev-info);
+		background: var(--color-sev-info-bg);
+	}
+	.warn {
+		color: var(--color-sev-warn);
+		background: var(--color-sev-warn-bg);
+	}
+	.error {
+		color: var(--color-sev-error);
+		background: var(--color-sev-error-bg);
+	}
+	.critical {
+		color: var(--color-sev-critical);
+		background: var(--color-sev-critical-bg);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Skeleton.svelte b/web/src/lib/components/ui/Skeleton.svelte
new file mode 100644
index 0000000..4e741cb
--- /dev/null
+++ b/web/src/lib/components/ui/Skeleton.svelte
@@ -0,0 +1,34 @@
+<script lang="ts">
+	let { width = '100%', height = '1rem' }: { width?: string; height?: string } = $props();
+</script>
+
+<span class="skeleton" style:width style:height></span>
+
+<style>
+	.skeleton {
+		display: block;
+		border-radius: var(--radius-sm);
+		background: linear-gradient(
+			90deg,
+			var(--color-surface-raised) 25%,
+			var(--color-border) 50%,
+			var(--color-surface-raised) 75%
+		);
+		background-size: 200% 100%;
+		animation: shimmer 1.4s ease-in-out infinite;
+	}
+	@media (prefers-reduced-motion: reduce) {
+		.skeleton {
+			animation: none;
+			background: var(--color-surface-raised);
+		}
+	}
+	@keyframes shimmer {
+		0% {
+			background-position: 200% 0;
+		}
+		100% {
+			background-position: -200% 0;
+		}
+	}
+</style>
diff --git a/web/src/lib/components/ui/Table.svelte b/web/src/lib/components/ui/Table.svelte
new file mode 100644
index 0000000..eed4266
--- /dev/null
+++ b/web/src/lib/components/ui/Table.svelte
@@ -0,0 +1,52 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	// A thin styling wrapper, not a data grid -- real <table> markup
+	// underneath (native semantics matter for screen readers), density-
+	// aware row height/padding from tokens.css's --row-* variables.
+	// Column sort/resize (task 6) layers on top of this later; this just
+	// establishes the shared chrome every table in the app should share.
+	let { children }: { children: Snippet } = $props();
+</script>
+
+<div class="scroll">
+	<table class="ui-table">
+		{@render children()}
+	</table>
+</div>
+
+<style>
+	.scroll {
+		overflow-x: auto;
+	}
+	table {
+		width: 100%;
+		border-collapse: collapse;
+		font-family: var(--font-mono);
+		font-size: var(--text-base);
+	}
+	:global(.ui-table thead th) {
+		text-align: left;
+		font-family: var(--font-ui);
+		font-size: var(--text-xs);
+		font-weight: var(--font-weight-medium);
+		text-transform: uppercase;
+		letter-spacing: 0.04em;
+		color: var(--color-text-muted);
+		padding: var(--space-2) var(--row-padding-x);
+		border-bottom: 1px solid var(--color-border);
+		white-space: nowrap;
+	}
+	:global(.ui-table tbody td) {
+		padding: var(--row-padding-y) var(--row-padding-x);
+		border-bottom: 1px solid var(--color-border);
+		color: var(--color-text);
+		vertical-align: middle;
+	}
+	:global(.ui-table tbody tr:last-child td) {
+		border-bottom: none;
+	}
+	:global(.ui-table tbody tr:hover td) {
+		background: var(--color-surface-raised);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Tabs.svelte b/web/src/lib/components/ui/Tabs.svelte
new file mode 100644
index 0000000..ce63506
--- /dev/null
+++ b/web/src/lib/components/ui/Tabs.svelte
@@ -0,0 +1,74 @@
+<script lang="ts">
+	// Renders the tab list only -- the caller renders each panel's content
+	// (conditionally, on `active`) and is responsible for
+	// id="panel-{tab.id}" aria-labelledby="tab-{tab.id}" on it. Keeps this
+	// component decoupled from what a panel's content actually is.
+	type Tab = { id: string; label: string };
+
+	let {
+		tabs,
+		active = $bindable('')
+	}: {
+		tabs: Tab[];
+		active?: string;
+	} = $props();
+
+	$effect(() => {
+		if (!active && tabs.length) active = tabs[0].id;
+	});
+
+	function onKeydown(e: KeyboardEvent) {
+		const i = tabs.findIndex((t) => t.id === active);
+		if (e.key === 'ArrowRight') {
+			active = tabs[(i + 1) % tabs.length].id;
+			e.preventDefault();
+		} else if (e.key === 'ArrowLeft') {
+			active = tabs[(i - 1 + tabs.length) % tabs.length].id;
+			e.preventDefault();
+		}
+	}
+</script>
+
+<div role="tablist" tabindex="-1" class="tablist" onkeydown={onKeydown}>
+	{#each tabs as tab (tab.id)}
+		<button
+			role="tab"
+			id="tab-{tab.id}"
+			aria-selected={active === tab.id}
+			aria-controls="panel-{tab.id}"
+			tabindex={active === tab.id ? 0 : -1}
+			class="tab"
+			class:active={active === tab.id}
+			onclick={() => (active = tab.id)}
+		>
+			{tab.label}
+		</button>
+	{/each}
+</div>
+
+<style>
+	.tablist {
+		display: flex;
+		gap: var(--space-1);
+		border-bottom: 1px solid var(--color-border);
+	}
+	.tab {
+		background: none;
+		border: none;
+		border-bottom: 2px solid transparent;
+		color: var(--color-text-muted);
+		font-family: var(--font-ui);
+		font-size: var(--text-base);
+		font-weight: var(--font-weight-medium);
+		padding: var(--space-2) var(--space-3);
+		cursor: pointer;
+		margin-bottom: -1px;
+	}
+	.tab:hover {
+		color: var(--color-text);
+	}
+	.tab.active {
+		color: var(--color-text);
+		border-bottom-color: var(--color-accent);
+	}
+</style>
diff --git a/web/src/lib/components/ui/Tooltip.svelte b/web/src/lib/components/ui/Tooltip.svelte
new file mode 100644
index 0000000..6aed41c
--- /dev/null
+++ b/web/src/lib/components/ui/Tooltip.svelte
@@ -0,0 +1,46 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	let { text, children, id }: { text: string; children: Snippet; id: string } = $props();
+</script>
+
+<span class="wrap">
+	<span aria-describedby={id} class="trigger">
+		{@render children()}
+	</span>
+	<span role="tooltip" {id} class="tip">{text}</span>
+</span>
+
+<style>
+	.wrap {
+		position: relative;
+		display: inline-flex;
+	}
+	.tip {
+		position: absolute;
+		bottom: calc(100% + var(--space-2));
+		left: 50%;
+		transform: translateX(-50%) translateY(2px);
+		background: var(--color-surface-raised);
+		border: 1px solid var(--color-border);
+		color: var(--color-text);
+		font-size: var(--text-xs);
+		padding: var(--space-1) var(--space-2);
+		border-radius: var(--radius-sm);
+		white-space: nowrap;
+		box-shadow: var(--shadow-sm);
+		opacity: 0;
+		visibility: hidden;
+		pointer-events: none;
+		transition:
+			opacity 0.1s ease,
+			transform 0.1s ease;
+		z-index: 20;
+	}
+	.wrap:hover .tip,
+	.wrap:focus-within .tip {
+		opacity: 1;
+		visibility: visible;
+		transform: translateX(-50%) translateY(0);
+	}
+</style>
diff --git a/web/src/lib/components/ui/index.ts b/web/src/lib/components/ui/index.ts
new file mode 100644
index 0000000..95247f7
--- /dev/null
+++ b/web/src/lib/components/ui/index.ts
@@ -0,0 +1,12 @@
+export { default as Button } from './Button.svelte';
+export { default as Input } from './Input.svelte';
+export { default as Select } from './Select.svelte';
+export { default as Badge } from './Badge.svelte';
+export { default as SeverityBadge } from './SeverityBadge.svelte';
+export { default as Table } from './Table.svelte';
+export { default as Card } from './Card.svelte';
+export { default as Modal } from './Modal.svelte';
+export { default as Tooltip } from './Tooltip.svelte';
+export { default as Tabs } from './Tabs.svelte';
+export { default as Skeleton } from './Skeleton.svelte';
+export { default as EmptyState } from './EmptyState.svelte';
diff --git a/web/src/routes/+layout.svelte b/web/src/routes/+layout.svelte
index 02999b3..cc1f0fb 100644
--- a/web/src/routes/+layout.svelte
+++ b/web/src/routes/+layout.svelte
@@ -1,10 +1,12 @@
 <script lang="ts">
+	import '$lib/styles/app.css';
 	import favicon from '$lib/assets/favicon.svg';
+	import NavSidebar from '$lib/components/NavSidebar.svelte';
+	import CommandPalette from '$lib/components/CommandPalette.svelte';
 
-	// Phase 3: dashboards + alerts routes added, so there's now more than
-	// one page -- a minimal nav replaces the previous "no nav, one page"
-	// layout.
 	let { children } = $props();
+	let paletteOpen = $state(false);
+	let mobileNavOpen = $state(false);
 </script>
 
 <svelte:head>
@@ -12,30 +14,62 @@
 	<link rel="icon" href={favicon} />
 </svelte:head>
 
-<nav>
-	<a href="/">Query</a>
-	<a href="/dashboards">Dashboards</a>
-	<a href="/alerts">Alerts</a>
-	<a href="/settings">Settings</a>
-</nav>
+<div class="shell">
+	<NavSidebar
+		onOpenPalette={() => (paletteOpen = true)}
+		mobileOpen={mobileNavOpen}
+		onCloseMobile={() => (mobileNavOpen = false)}
+	/>
+	<div class="main-col">
+		<button type="button" class="menu-toggle" onclick={() => (mobileNavOpen = true)} aria-label="Open menu">
+			☰
+		</button>
+		<div class="page">
+			{@render children()}
+		</div>
+	</div>
+</div>
 
-{@render children()}
+<CommandPalette bind:open={paletteOpen} />
 
 <style>
-	nav {
-		font-family: system-ui, sans-serif;
-		max-width: 960px;
-		margin: 1rem auto 0;
-		padding: 0 1rem;
-		display: flex;
-		gap: 1.25rem;
+	.shell {
+		display: grid;
+		grid-template-columns: 15rem 1fr;
+		min-height: 100vh;
 	}
-	nav a {
-		color: #06c;
-		text-decoration: none;
-		font-size: 0.9rem;
+	.main-col {
+		min-width: 0;
 	}
-	nav a:hover {
-		text-decoration: underline;
+	.page {
+		padding: var(--space-6);
+		min-width: 0;
+	}
+	.menu-toggle {
+		display: none;
+	}
+
+	@media (max-width: 860px) {
+		.shell {
+			grid-template-columns: 1fr;
+		}
+		.menu-toggle {
+			display: block;
+			position: sticky;
+			top: 0;
+			z-index: 10;
+			width: 100%;
+			text-align: left;
+			background: var(--color-surface);
+			border: none;
+			border-bottom: 1px solid var(--color-border);
+			color: var(--color-text);
+			font-size: var(--text-md);
+			padding: var(--space-3) var(--space-4);
+			cursor: pointer;
+		}
+		.page {
+			padding: var(--space-4);
+		}
 	}
 </style>
diff --git a/web/src/routes/data-sources/+page.svelte b/web/src/routes/data-sources/+page.svelte
new file mode 100644
index 0000000..9a06f75
--- /dev/null
+++ b/web/src/routes/data-sources/+page.svelte
@@ -0,0 +1,54 @@
+<script lang="ts">
+	import { Card } from '$lib/components/ui';
+	import { enterpriseAuthBase } from '$lib/api';
+</script>
+
+<main class="page">
+	<h1>Data Sources</h1>
+	<p class="lede">
+		Every tenant has exactly one data source today — its own ClickHouse database and Tantivy
+		index, provisioned together when the tenant is created. There's nothing to configure yet.
+	</p>
+
+	<Card title="Current data source">
+		{#if enterpriseAuthBase}
+			<p>
+				Your queries run against your tenant's dedicated ClickHouse database and Tantivy index —
+				never a shared one. See <a href="/settings">Settings</a> for SSO and tenant configuration.
+			</p>
+		{:else}
+			<p>
+				This deployment isn't running in multi-tenant mode, so there's one data source for the
+				whole instance — the default ClickHouse database and Tantivy index every query already
+				runs against.
+			</p>
+		{/if}
+	</Card>
+
+	<p class="note">
+		Multiple data sources per tenant — a second ClickHouse cluster, a read replica, an external
+		source — is real future work, not something this page is hiding. The
+		<code>data_sources</code> table this reads from was already built with that in mind (see
+		<code>/docs/phase-4-rbac-design.md</code>).
+	</p>
+</main>
+
+<style>
+	.page {
+		max-width: 42rem;
+		display: flex;
+		flex-direction: column;
+		gap: var(--space-4);
+	}
+	h1 {
+		font-size: var(--text-xl);
+	}
+	.lede {
+		color: var(--color-text-muted);
+		margin: 0;
+	}
+	.note {
+		font-size: var(--text-sm);
+		color: var(--color-text-muted);
+	}
+</style>
diff --git a/web/src/routes/select-tenant/+page.svelte b/web/src/routes/select-tenant/+page.svelte
index bd755c9..629e8ef 100644
--- a/web/src/routes/select-tenant/+page.svelte
+++ b/web/src/routes/select-tenant/+page.svelte
@@ -83,10 +83,8 @@
 
 <style>
 	main {
-		font-family: system-ui, sans-serif;
-		max-width: 480px;
-		margin: 3rem auto;
-		padding: 0 1rem;
+		max-width: 30rem;
+		margin: var(--space-8) auto;
 	}
 	ul {
 		list-style: none;
@@ -94,23 +92,25 @@
 		padding: 0;
 		display: flex;
 		flex-direction: column;
-		gap: 0.5rem;
+		gap: var(--space-2);
 	}
 	button {
 		width: 100%;
 		display: flex;
 		align-items: center;
-		gap: 0.75rem;
-		padding: 0.75rem 1rem;
-		font-size: 1rem;
+		gap: var(--space-3);
+		padding: var(--space-3) var(--space-4);
+		font-size: var(--text-md);
+		font-family: var(--font-ui);
 		text-align: left;
-		background: #fff;
-		border: 1px solid #ccc;
-		border-radius: 6px;
+		background: var(--color-surface);
+		color: var(--color-text);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-md);
 		cursor: pointer;
 	}
 	button:hover:not(:disabled) {
-		border-color: #06c;
+		border-color: var(--color-accent);
 	}
 	button:disabled {
 		cursor: default;
@@ -118,18 +118,18 @@
 	}
 	.name {
 		flex: 1;
-		font-weight: 600;
+		font-weight: var(--font-weight-medium);
 	}
 	.role {
-		color: #666;
-		font-size: 0.85rem;
+		color: var(--color-text-muted);
+		font-size: var(--text-sm);
 		text-transform: capitalize;
 	}
 	.error {
-		color: #b00020;
+		color: var(--color-danger);
 	}
 	.note {
-		color: #666;
-		font-size: 0.85rem;
+		color: var(--color-text-muted);
+		font-size: var(--text-sm);
 	}
 </style>
diff --git a/web/src/routes/settings/+page.svelte b/web/src/routes/settings/+page.svelte
index fc580a6..ebdabf8 100644
--- a/web/src/routes/settings/+page.svelte
+++ b/web/src/routes/settings/+page.svelte
@@ -1,5 +1,7 @@
 <script lang="ts">
 	import { getAuthFeatures, enterpriseAuthBase, type AuthFeatures } from '$lib/api';
+	import { getTheme, setTheme, type Theme } from '$lib/theme.svelte';
+	import { getDensity, setDensity, type Density } from '$lib/density.svelte';
 
 	let loading = $state(true);
 	let features = $state<AuthFeatures>({ sso_configured: false, oidc_enabled: false, saml_enabled: false });
@@ -10,18 +12,60 @@
 		loading = false;
 	}
 	load();
+
+	const themeOptions: { value: Theme; label: string; hint: string }[] = [
+		{ value: 'dark', label: 'Dark', hint: 'Default' },
+		{ value: 'light', label: 'Light', hint: '' },
+		{ value: 'system', label: 'System', hint: 'Follow OS setting' }
+	];
+	const densityOptions: { value: Density; label: string; hint: string }[] = [
+		{ value: 'comfortable', label: 'Comfortable', hint: 'Dashboards, forms' },
+		{ value: 'compact', label: 'Compact', hint: 'Log tables, results' }
+	];
 </script>
 
 <main>
 	<h1>Settings</h1>
 
+	<section>
+		<h2>Appearance</h2>
+		<div class="option-group" role="radiogroup" aria-label="Theme">
+			{#each themeOptions as opt (opt.value)}
+				<button
+					type="button"
+					class="option"
+					class:selected={getTheme() === opt.value}
+					aria-pressed={getTheme() === opt.value}
+					onclick={() => setTheme(opt.value)}
+				>
+					<span class="option-label">{opt.label}</span>
+					{#if opt.hint}<span class="option-hint">{opt.hint}</span>{/if}
+				</button>
+			{/each}
+		</div>
+		<div class="option-group" role="radiogroup" aria-label="Row density">
+			{#each densityOptions as opt (opt.value)}
+				<button
+					type="button"
+					class="option"
+					class:selected={getDensity() === opt.value}
+					aria-pressed={getDensity() === opt.value}
+					onclick={() => setDensity(opt.value)}
+				>
+					<span class="option-label">{opt.label}</span>
+					<span class="option-hint">{opt.hint}</span>
+				</button>
+			{/each}
+		</div>
+	</section>
+
 	<section>
 		<h2>Core</h2>
 		<p>Single-tenant deployment settings live here. Nothing configurable yet.</p>
 	</section>
 
 	{#if loading}
-		<p>Loading…</p>
+		<p class="muted">Loading…</p>
 	{:else if features.sso_configured}
 		<section>
 			<h2>Single sign-on</h2>
@@ -48,19 +92,66 @@
 
 <style>
 	main {
-		font-family: system-ui, sans-serif;
-		max-width: 960px;
-		margin: 2rem auto;
-		padding: 0 1rem;
+		max-width: 40rem;
+	}
+	h1 {
+		font-size: var(--text-xl);
+		margin-bottom: var(--space-5);
 	}
 	section {
-		margin-bottom: 1.5rem;
+		margin-bottom: var(--space-6);
 	}
 	h2 {
-		font-size: 1.1rem;
+		font-size: var(--text-md);
+		margin-bottom: var(--space-3);
+	}
+	.muted {
+		color: var(--color-text-muted);
 	}
 	.note {
-		color: #666;
-		font-size: 0.85rem;
+		color: var(--color-text-muted);
+		font-size: var(--text-sm);
+	}
+	.option-group {
+		display: flex;
+		gap: var(--space-2);
+		margin-bottom: var(--space-3);
+	}
+	.option {
+		flex: 1;
+		display: flex;
+		flex-direction: column;
+		align-items: flex-start;
+		gap: var(--space-1);
+		padding: var(--space-3);
+		border: 1px solid var(--color-border);
+		border-radius: var(--radius-md);
+		background: var(--color-surface);
+		cursor: pointer;
+		text-align: left;
+	}
+	.option:hover {
+		border-color: var(--color-border-strong);
+	}
+	.option.selected {
+		border-color: var(--color-accent);
+		background: color-mix(in srgb, var(--color-accent) 8%, var(--color-surface));
+	}
+	.option-label {
+		font-weight: var(--font-weight-medium);
+		color: var(--color-text);
+	}
+	.option-hint {
+		font-size: var(--text-xs);
+		color: var(--color-text-muted);
+	}
+	/* The accent-tinted .selected background is *lighter* than plain
+	   --color-surface, which quietly drops --color-text-muted below
+	   4.5:1 (axe-core's color-contrast check caught this at 4.4:1) --
+	   fixed by using the full-strength --color-text on that lighter
+	   background specifically, not by changing the shared muted token
+	   everywhere else it still passes correctly. */
+	.option.selected .option-hint {
+		color: var(--color-text);
 	}
 </style>