Dashboard: every number leads somewhere, real counts, and new charts

- Cards and charts link to the page they're about: pending messages to the
  queue, bans to blocked IPs, report warnings to the reports, and so on,
  shown only to viewers who may open that page.
- A one-line status under the greeting: what needs a look (failed tasks,
  messages retrying, recipients given up on) or, when nothing does, what's
  there. Each phrase is a link.
- Counts from the server's own objects stand in for live metrics it can't
  report, and a live number with no source reads as unknown, not zero.
- Who uses the space: a treemap of people sized by storage, colored by how
  near their quota they are, each tile opening the account.
- Where mail is waiting: queued recipients by destination, split into
  waiting, retrying and given up, each row opening the filtered queue.
- The weekly rhythm: messages by hour and weekday, shown once metric
  history exists.
- Dashboard tabs are titled by their label.

src/features/dashboard/rhythm.ts

@@ -0,0 +1,28 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { Metric } from './types/metrics';
+
+/** Received plus sent: every message the server handled. */
+export const RHYTHM_METRICS = [
+  'queue.message-queued',
+  'queue.authenticated-message-queued',
+  'queue.dsn-queued',
+  'queue.report-queued',
+];
+
+/** Sum the samples into a 7×24 grid, Monday first, in the viewer's time zone. */
+export function weeklyGrid(samples: Metric[], metrics: string[] = RHYTHM_METRICS): number[][] {
+  const want = new Set(metrics);
+  const grid = Array.from({ length: 7 }, () => new Array<number>(24).fill(0));
+  for (const s of samples) {
+    if (!want.has(s.metric) || !s.timestamp) continue;
+    const d = new Date(s.timestamp);
+    if (Number.isNaN(d.getTime())) continue;
+    grid[(d.getDay() + 6) % 7][d.getHours()] += s.count;
+  }
+  return grid;
+}