Replace the notifications stub with real FCM notifications

Problem

Raised in the placement meeting as a P1, covering three cases: personal status updates (interview shortlist, accepted), deadline reminders, and company added or updated.

The app has none of it. The notifications screen renders five hardcoded fake rows, nothing navigates to it, and there is no messaging dependency.

Most of the server side already exists and is simply unused:

• The online-admin app already emits profile-announcement and application status-update notifications.
• Token registration is POST /api/notifications/token/, authenticated by JWT via client_identifier.
• iOS push does not work server-side: the FCM helper builds only AndroidConfig and WebpushConfig, never APNSConfig.
• Deadline notifications do not exist anywhere.

Where

• lib/screens/notifications/notificationsScreen.dart:17-33 (five hardcoded rows)
• lib/services/routing/placement_routes.dart:33-34 (/notifs registered, never navigated to)
• pubspec.yaml (no firebase_messaging)
• omniport-service-notifications/utils/fcm/fcm.py:29, 52 (no APNS)
• omniport-service-notifications/views/token.py:28-31

Expected

Push on shortlist and accept, push on a new or updated company, plus a real in-app notification list.

Fix sketch

• Add firebase_messaging; register the FCM token against /api/notifications/token/ after login and unregister on logout.
• Replace the stub with a real fetch, and add an entry point to it from the profile screen.
• iOS push and deadline notifications need backend work first and are tracked separately.

Start with lib/screens/notifications/notificationsScreen.dart:17-33, pubspec.yaml, and lib/services/routing/placement_routes.dart:33-34; trace the existing profile entry points and notification data flow. Then inspect omniport-service-notifications/views/token.py:28-31 and utils/fcm/fcm.py:29,52. Done means token registration works across login/logout, the screen shows fetched notifications, profile navigation reaches it, and shortlist, acceptance, and company updates produce push notifications.