feat: implement FCM push notifications via firebase_messaging

- Add firebase_core + firebase_messaging to pubspec.yaml
- Initialize Firebase in main.dart before runApp
- NotificationBloc: request permission, get FCM token, register with
  backend (PATCH /users/me/fcm-token), show local notification on
  foreground messages, refresh token on rotation
- app_view.dart: call initializePushNotifications() on authenticated state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/blocs/notification_bloc/notification_bloc.dart

@@ -1,14 +1,22 @@
+import 'dart:convert';
 import 'dart:developer';
-
+import 'package:firebase_messaging/firebase_messaging.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:equatable/equatable.dart';
+import 'package:http/http.dart' as http;
+import 'package:shared_preferences/shared_preferences.dart';
 import 'package:user_repository/user_repository.dart';
+import 'package:prosappco/constansts.dart' show API_BASE_URL;
 
 part 'notification_event.dart';
 part 'notification_state.dart';
 
-// Stub: Firebase messaging removed. Background handler is no longer needed.
-Future<void> firebaseMessagingBackgroundHandler(dynamic message) async {}
+// Handles FCM messages when app is terminated/background
+@pragma('vm:entry-point')
+Future<void> firebaseMessagingBackgroundHandler(RemoteMessage message) async {
+  // Local notification shown by the system tray automatically for data-only
+  // messages; nothing extra needed here.
+}
 
 class NotificationBloc extends Bloc<NotificationEvent, NotificationState> {
   final Future<void> Function() requestLocalNotificationPermission;
@@ -31,6 +39,60 @@ class NotificationBloc extends Bloc<NotificationEvent, NotificationState> {
     emit(state.copyWith(status: event.status));
   }
 
+  // Call once after login to register the FCM token and listen for foreground messages.
+  Future<void> initializePushNotifications() async {
+    try {
+      final messaging = FirebaseMessaging.instance;
+      final settings = await messaging.requestPermission();
+      add(NotificationStatusChanged(
+        settings.authorizationStatus == AuthorizationStatus.authorized ||
+                settings.authorizationStatus == AuthorizationStatus.provisional
+            ? AuthorizationStatus.authorized
+            : AuthorizationStatus.denied,
+      ));
+
+      final token = await messaging.getToken();
+      if (token != null) await _registerToken(token);
+
+      // Refresh token (e.g. after reinstall)
+      messaging.onTokenRefresh.listen(_registerToken);
+
+      // Show local notification when app is in foreground
+      FirebaseMessaging.onMessage.listen((RemoteMessage message) {
+        final n = message.notification;
+        if (n != null) {
+          showLocalNotification(
+            id: message.hashCode,
+            title: n.title,
+            body: n.body,
+            data: jsonEncode(message.data),
+          );
+        }
+      });
+    } catch (e) {
+      log('NotificationBloc.initializePushNotifications error: $e');
+    }
+  }
+
+  Future<void> _registerToken(String token) async {
+    try {
+      final prefs = await SharedPreferences.getInstance();
+      final jwt = prefs.getString('token');
+      if (jwt == null) return;
+      await http.patch(
+        Uri.parse('$API_BASE_URL/users/me/fcm-token'),
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': 'Bearer $jwt',
+        },
+        body: jsonEncode({'token': token}),
+      );
+      log('FCM token registered');
+    } catch (e) {
+      log('NotificationBloc._registerToken error: $e');
+    }
+  }
+
   void requestPermission() async {
     try {
       await requestLocalNotificationPermission();