ihasmail 2.0: rebuild as Stalwart-first JMAP webmail

Replace the FastAPI/HTMX prototype with a Node/Hono session proxy and a
React 19/Vite SPA. Mail (conversation view, search operators, labels,
sanitised HTML, privacy image proxy, invites, undo send, templates),
calendar (month/week/day/agenda, invites, free/busy, categories,
context menus), contacts (JSContact, groups, vCard), files, Sieve filter
builder (incl. filter-from-message with retroactive apply), vacation,
identities with default + Reply-To, PWA/mobile layout, push via SSE,
in-memory mock Stalwart for dev, Docker + CI.

web/src/lib/storage.ts

@@ -0,0 +1,42 @@
+const PREFIX = "ihasmail:";
+
+export function loadJson<T>(key: string, fallback: T): T {
+  try {
+    const raw = localStorage.getItem(PREFIX + key);
+    if (raw == null) return fallback;
+    return { ...fallback, ...(JSON.parse(raw) as T) };
+  } catch {
+    return fallback;
+  }
+}
+
+export function loadRaw<T>(key: string, fallback: T): T {
+  try {
+    const raw = localStorage.getItem(PREFIX + key);
+    if (raw == null) return fallback;
+    return JSON.parse(raw) as T;
+  } catch {
+    return fallback;
+  }
+}
+
+export function saveJson(key: string, value: unknown): void {
+  try {
+    localStorage.setItem(PREFIX + key, JSON.stringify(value));
+  } catch {
+    /* quota exceeded or private mode */
+  }
+}
+
+export function removeKey(key: string): void {
+  try {
+    localStorage.removeItem(PREFIX + key);
+  } catch {
+    /* ignore */
+  }
+}
+
+/** Namespaced per account so multiple logins on one browser don't collide. */
+export function accountKey(accountId: string | null | undefined, key: string): string {
+  return `${accountId ?? "anon"}:${key}`;
+}