feat: Implement Firebase push notifications with support for flavor-specific configurations.

lib/main.dart

@@ -1,3 +1,4 @@
+import 'package:firebase_core/firebase_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:real_estate_mobile/config/app_config.dart';
@@ -7,6 +8,7 @@ import 'package:real_estate_mobile/routing/app_router.dart';
 Future<void> mainCommon(Flavor flavor) async {
   WidgetsFlutterBinding.ensureInitialized();
   await AppConfig.init(flavor);
+  await Firebase.initializeApp();
   runApp(const ProviderScope(child: MyApp()));
 }