Consolidate Boundaries + History under the account; sectioned /account

The inline Boundaries/History panels lived on the home page, so opening them while
scrolled left you stranded. Move everything "yours" behind the account icon:

- Home header slims to: Saved (opens a right-side flyout, signed-in) · shield
  (Boundaries indicator — filled when active — linking to the Boundaries section) ·
  avatar. The inline panels + the home "saved" view are gone.
- /account is now a sectioned hub (left sidebar on desktop, top tabs on mobile),
  OPEN TO EVERYONE with each section self-gating: Profile (sign-in), Saved (sign-in),
  History (device/account), Boundaries (device/account), Admin (admins). This keeps
  Boundaries/History usable without an account (they're device-local) while
  consolidating the UI — and every section loads at the top, fixing the scroll bug.
- Lift Calm Filters and History into shared stores (prefs.svelte.js, history.svelte.js)
  so the home feed (applies/records) and the account page (edits/manages) share one
  source of truth. New SavedFlyout component. Card boundary actions only render when a
  handler is provided.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/prefs.svelte.js

@@ -0,0 +1,47 @@
+// Reactive Calm Filters (Boundaries), shared across the home feed (which applies
+// them) and the account page (which edits them). One source of truth.
+import * as P from './prefs.js';
+import { auth } from './auth.svelte.js';
+import { getJSON, putJSON } from './api.js';
+
+export const prefs = $state({ data: P.blank(), ready: false });
+
+export function initPrefs() {
+  if (prefs.ready) return;
+  prefs.data = P.load();
+  prefs.ready = true;
+}
+
+export function active() {
+  return P.active(prefs.data);
+}
+
+export function persistPrefs() {
+  P.save(prefs.data);
+  if (auth.user) putJSON('/api/prefs', { prefs: prefs.data }).catch(() => {});
+}
+
+// Card actions ("Not today" / "Less like this" / "Hide topic").
+export function applyPrefAction(kind, value) {
+  P[kind]?.(prefs.data, value);
+  prefs.data = { ...prefs.data };
+  persistPrefs();
+}
+
+// On sign-in: adopt the account's prefs if present, else seed them from this device.
+export async function syncPrefsOnLogin() {
+  try {
+    const res = await getJSON('/api/prefs');
+    if (res && res.prefs) {
+      const incoming = Object.assign(P.blank(), res.prefs);
+      if (JSON.stringify(incoming) !== JSON.stringify(prefs.data)) {
+        prefs.data = incoming;
+        P.save(prefs.data);
+      }
+    } else {
+      await putJSON('/api/prefs', { prefs: prefs.data });
+    }
+  } catch {
+    /* best-effort */
+  }
+}