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/firebase_options.dart

@@ -0,0 +1,77 @@
+// File generated by FlutterFire CLI.
+// ignore_for_file: type=lint
+import 'package:firebase_core/firebase_core.dart' show FirebaseOptions;
+import 'package:flutter/foundation.dart'
+    show defaultTargetPlatform, kIsWeb, TargetPlatform;
+
+/// Default [FirebaseOptions] for use with your Firebase apps.
+///
+/// Example:
+/// ```dart
+/// import 'firebase_options.dart';
+/// // ...
+/// await Firebase.initializeApp(
+///   options: DefaultFirebaseOptions.currentPlatform,
+/// );
+/// ```
+class DefaultFirebaseOptions {
+  static FirebaseOptions get currentPlatform {
+    if (kIsWeb) {
+      throw UnsupportedError(
+        'DefaultFirebaseOptions have not been configured for web - '
+        'you can reconfigure this by running the FlutterFire CLI again.',
+      );
+    }
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+        return android;
+      case TargetPlatform.iOS:
+        return ios;
+      case TargetPlatform.macOS:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for macos - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.windows:
+        return windows;
+      case TargetPlatform.linux:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for linux - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      default:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions are not supported for this platform.',
+        );
+    }
+  }
+
+  static const FirebaseOptions android = FirebaseOptions(
+    apiKey: 'AIzaSyAON_ol0Jr34tKbETvdDK9JCQdKNawxBeQ',
+    appId: '1:521527250907:android:be3db7fc84f053ec7da1fe',
+    messagingSenderId: '521527250907',
+    projectId: 'travelmate-a47f5',
+    storageBucket: 'travelmate-a47f5.firebasestorage.app',
+  );
+
+  static const FirebaseOptions ios = FirebaseOptions(
+    apiKey: 'AIzaSyBFaSzvcvO8qg7El-2jRf7WctZIMKNA4-I',
+    appId: '1:521527250907:ios:64b41be39c54db1c7da1fe',
+    messagingSenderId: '521527250907',
+    projectId: 'travelmate-a47f5',
+    storageBucket: 'travelmate-a47f5.firebasestorage.app',
+    iosClientId: '521527250907-3i1qe2656eojs8k9hjdi573j09i9p41m.apps.googleusercontent.com',
+    iosBundleId: 'com.example.travelMate',
+  );
+
+  static const FirebaseOptions windows = FirebaseOptions(
+    apiKey: 'AIzaSyC4t-WOvp22zns9b9t58urznsNAhSHRAag',
+    appId: '1:521527250907:web:53ff98bcdb8c218f7da1fe',
+    messagingSenderId: '521527250907',
+    projectId: 'travelmate-a47f5',
+    authDomain: 'travelmate-a47f5.firebaseapp.com',
+    storageBucket: 'travelmate-a47f5.firebasestorage.app',
+    measurementId: 'G-J246Y7J61M',
+  );
+
+}