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/services/auth_service.dart

@@ -0,0 +1,68 @@
+import 'package:firebase_auth/firebase_auth.dart';
+
+class AuthService {
+  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
+
+  User? get currentUser => firebaseAuth.currentUser;
+
+  Stream<User?> get authStateChanges => firebaseAuth.authStateChanges();
+
+  Future<UserCredential> signIn({
+    required String email,
+    required String password
+  }) async {
+    return await firebaseAuth.signInWithEmailAndPassword(
+        email: email, password: password);
+  }
+
+  Future<UserCredential> createAccount({
+      required String email, 
+      required String password
+    }) async {
+    return await firebaseAuth.createUserWithEmailAndPassword(
+        email: email, password: password);
+  }
+
+  Future<void> signOut() async {
+    await firebaseAuth.signOut();
+  }
+
+  Future<void> resetPassword(String email) async {
+    await firebaseAuth.sendPasswordResetEmail(email: email);
+  }
+
+  Future<void> updateDisplayName({
+    required String displayName,
+  }) async {
+    await currentUser!.updateDisplayName(displayName);
+  }
+
+  Future<void> deleteAccount({
+    required String password,
+    required String email,
+  }) async {
+    // Re-authenticate the user
+    AuthCredential credential =
+        EmailAuthProvider.credential(email: email, password: password);
+    await currentUser!.reauthenticateWithCredential(credential);
+
+    // Delete the user
+    await currentUser!.delete();
+    await firebaseAuth.signOut();
+  }
+
+  Future<void> resetPasswordFromCurrentPassword({
+    required String currentPassword,
+    required String newPassword,
+    required String email,
+  }) async {
+    // Re-authenticate the user
+    AuthCredential credential =
+        EmailAuthProvider.credential(email: email, password: currentPassword);
+    await currentUser!.reauthenticateWithCredential(credential);
+
+    // Update the password
+    await currentUser!.updatePassword(newPassword);
+  }
+  
+}