feat: Integrate Firebase Authentication and Firestore

- Added Firebase configuration to Android and iOS projects.
- Created `google-services.json` and `GoogleService-Info.plist` for Firebase setup.
- Implemented `AuthService` for handling user authentication with Firebase.
- Updated `UserProvider` to manage user data with Firestore.
- Refactored `ProfileContent`, `LoginPage`, and `SignUpPage` to use the new authentication service.
- Removed the old `UserService` and replaced it with Firestore-based user management.
- Added Firebase options in `firebase_options.dart` for platform-specific configurations.
- Updated dependencies in `pubspec.yaml` for Firebase packages.

lib/main.dart

@@ -6,8 +6,14 @@ import 'pages/login.dart';
 import 'pages/home.dart';
 import 'providers/theme_provider.dart';
 import 'providers/user_provider.dart';
+import 'package:firebase_core/firebase_core.dart';
+import 'firebase_options.dart';
 
-void main() {
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Firebase.initializeApp(
+  options: DefaultFirebaseOptions.currentPlatform,
+);
   runApp(
     MultiProvider(
       providers: [