Integrate Firebase Authentication and Streamline Auth Flow in main.dart

This commit integrates Firebase Authentication into the application and refactors the `main.dart` file to streamline the user authentication flow. The application will now automatically switch between the main layout and the authentication UI based on the user's sign-in status.

- Added Firebase initialization to the `main()` function for Firebase Authentication.
- Replaced the home page in `MyApp` with a `StreamBuilder` that listens for Firebase auth state changes.
- Based on the auth state, the home page will either show `MainLayout` (if the user is signed in) or `FirebaseAuthView` (if the user is not signed in).
- Added necessary imports for the Firebase and authentication services.

frontend/lib/main.dart

@@ -1,6 +1,10 @@
+import 'package:auto_gpt_flutter_client/services/auth_service.dart';
+import 'package:auto_gpt_flutter_client/views/auth/firebase_auth_view.dart';
 import 'package:flutter/material.dart';
 import 'views/main_layout.dart';
 import 'package:provider/provider.dart';
+import 'package:firebase_core/firebase_core.dart';
+import 'package:firebase_auth/firebase_auth.dart';
 
 import 'package:auto_gpt_flutter_client/viewmodels/task_viewmodel.dart';
 import 'package:auto_gpt_flutter_client/viewmodels/chat_viewmodel.dart';
@@ -14,7 +18,20 @@ import 'package:auto_gpt_flutter_client/services/benchmark_service.dart';
 import 'package:auto_gpt_flutter_client/utils/rest_api_utility.dart';
 
 // TODO: Update documentation throughout project for consistency
-void main() {
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Firebase.initializeApp(
+    options: const FirebaseOptions(
+      apiKey: 'AIzaSyBvYLAK_A0uhFuVPQbTxUdVWbb_Lsur9cg',
+      authDomain: 'prod-auto-gpt.firebaseapp.com',
+      projectId: 'prod-auto-gpt',
+      storageBucket: 'prod-auto-gpt.appspot.com',
+      messagingSenderId: '387936576242',
+      appId: '1:387936576242:web:7536e0c50dd81b4dd7a66b',
+      measurementId: 'G-8PRS69JJRL',
+    ),
+  );
+
   runApp(
     MultiProvider(
       providers: [
@@ -48,29 +65,36 @@ void main() {
 class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    // Fetch services from providers
-    final chatService = Provider.of<ChatService>(context, listen: false);
-    final taskService = Provider.of<TaskService>(context, listen: false);
-    final benchmarkService =
-        Provider.of<BenchmarkService>(context, listen: false);
-    taskService.loadDeletedTasks();
-
     return MaterialApp(
       title: 'AutoGPT Flutter Client',
       theme: ThemeData(
         primarySwatch: Colors.blue,
       ),
-      home: MultiProvider(
-        providers: [
-          ChangeNotifierProvider(
-              create: (context) => ChatViewModel(chatService)),
-          ChangeNotifierProvider(
-              create: (context) => TaskViewModel(taskService)),
-          ChangeNotifierProvider(
-            create: (context) => SkillTreeViewModel(benchmarkService),
-          ),
-        ],
-        child: MainLayout(),
+      home: StreamBuilder<User?>(
+        stream: FirebaseAuth.instance.authStateChanges(),
+        builder: (context, snapshot) {
+          if (snapshot.connectionState == ConnectionState.waiting) {
+            return CircularProgressIndicator();
+          }
+          if (snapshot.hasData && snapshot.data != null) {
+            return MultiProvider(
+              providers: [
+                ChangeNotifierProvider(
+                    create: (context) => ChatViewModel(
+                        Provider.of<ChatService>(context, listen: false))),
+                ChangeNotifierProvider(
+                    create: (context) => TaskViewModel(
+                        Provider.of<TaskService>(context, listen: false))),
+                ChangeNotifierProvider(
+                  create: (context) => SkillTreeViewModel(
+                      Provider.of<BenchmarkService>(context, listen: false)),
+                ),
+              ],
+              child: MainLayout(),
+            ); // User is signed in
+          }
+          return FirebaseAuthView(); // User is not signed in, show auth UI
+        },
       ),
     );
   }