feat: county sync on monitor page + in-app notification system

- GET /api/eterra/counties — distinct county list from GisUat
- POST /api/eterra/sync-county — background sync all UATs in a county
  (TERENURI + CLADIRI + INTRAVILAN), magic mode for enriched UATs,
  concurrency guard, creates notification on completion
- In-app notification service (KeyValueStore, CRUD, unread count)
- GET/PATCH /api/notifications/app — list and mark-read endpoints
- NotificationBell component in header with popover + polling
- Monitor page: county select dropdown + SyncTestButton with customBody

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/core/notifications/index.ts

@@ -15,3 +15,12 @@ export {
   getAllPreferences,
   runDigest,
 } from "./notification-service";
+export {
+  createAppNotification,
+  getAppNotifications,
+  getUnreadCount,
+  markAsRead,
+  markAllAsRead,
+  type AppNotification,
+  type AppNotificationType,
+} from "./app-notifications";