feat: voice messages, offline queue, delivery ticks, volume slider, admin + scaling

- Voice messages: MediaRecorder → encrypted attachment, custom waveform
  player via OfflineAudioContext, 60s limit + live mic-level meter
- Offline message queue: localStorage outbox, exponential backoff retries,
  optimistic pending bubble with retry/discard
- Delivery indicator: message_deliveries table + RLS (reciprocal receipts),
  ✓ / ✓✓ / ✓✓-blue tick states, group-aware (all members must ack)
- Per-participant volume slider in calls via right-click tile menu,
  persisted to localStorage, applied to attached audio elements
- Group call scaling: grid up to 12 tiles with pagination,
  active-speaker auto-promotion in fullscreen
- Push notifications scaffolding: service worker, VAPID subscription
  registration, notify-push edge function skeleton
- Backup recovery code: 24-char base32 code (~120 bits entropy) as
  alternative decrypt path, restore UI with mode toggle
- Admin panel: conversations list, audit log (admin_audit_log table +
  admin_log_action RPC), audit entry on user flag toggle
- Search v2: sender filter, attachment-only toggle, date range
- Reactions pop animation (scale 0.4→1.15→1 on count change)
- Message list windowing (150 default, expand via IntersectionObserver)
- Stub cleanup: removed dead ScreenshareStub from CallParticipantTile

Fixes:
- Focus-triggered flicker: dropped window.focus listeners in three spots,
  throttled visibilitychange/online wake-refreshes to 30s, keep existing
  data visible during background re-syncs (no more spinner on every click)
- Voice attachment audio element collapsed to 0px on peer side — now
  forces 280px min-width on bubble

Migrations (push required):
  20260421000001_message_deliveries.sql
  20260421000002_admin_audit_log.sql

Server TODO:
  VAPID keys + notify-push edge function deploy

apps/desktop/src/context/AuthContext.tsx

@@ -20,6 +20,7 @@ import { useTranslation } from 'react-i18next';
 import { findExistingDevice } from '../lib/device';
 import { setSecretStoreUser } from '../lib/secretStore';
 import { supabase } from '../lib/supabase';
+import { registerWebPush } from '../lib/webPush';
 
 interface AuthContextValue {
   session: Session | null;
@@ -135,6 +136,13 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     });
   }, [session, refreshProfile, refreshDevice]);
 
+  // Best-effort web-push registration once we know the device id. No-op on
+  // Tauri (uses native notifications) or when VITE_VAPID_PUBLIC_KEY is unset.
+  useEffect(() => {
+    if (!device?.id) return;
+    void registerWebPush(device.id);
+  }, [device?.id]);
+
   const signOut = useCallback(async () => {
     await supabaseSignOut(supabase);
   }, []);