Enhance model and service documentation with detailed comments and descriptions

- Updated Group, Trip, User, and other model classes to include comprehensive documentation for better understanding and maintainability.
- Improved error handling and logging in services, including AuthService, ErrorService, and StorageService.
- Added validation and business logic explanations in ExpenseService and TripService.
- Refactored method comments to follow a consistent format across the codebase.
- Translated error messages and comments from French to English for consistency.

lib/main.dart

@@ -30,6 +30,10 @@ import 'pages/home.dart';
 import 'pages/signup.dart';
 import 'pages/resetpswd.dart';
 
+/// Entry point of the Travel Mate application.
+/// 
+/// This function initializes Flutter widgets, loads environment variables,
+/// initializes Firebase, and starts the application.
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
   await dotenv.load(fileName: ".env");
@@ -38,45 +42,63 @@ void main() async {
   runApp(const MyApp());
 }
 
+/// The root widget of the Travel Mate application.
+/// 
+/// This widget sets up the BLoC providers, repositories, and MaterialApp
+/// configuration. It manages the application's theme, routing, and global state.
 class MyApp extends StatelessWidget {
+  /// Creates the main application widget.
   const MyApp({super.key});
 
+  /// Builds the widget tree for the application.
+  /// 
+  /// Sets up repository providers for dependency injection, BLoC providers
+  /// for state management, and configures the MaterialApp with themes and routing.
   @override
   Widget build(BuildContext context) {
     return MultiRepositoryProvider(
       providers: [
+        // Authentication repository for handling user authentication
         RepositoryProvider<AuthRepository>(
           create: (context) => AuthRepository(),
         ),
+        // User repository for managing user data
         RepositoryProvider<UserRepository>(
           create: (context) => UserRepository(),
         ),
+        // Trip repository for managing travel trips
         RepositoryProvider<TripRepository>(
           create: (context) => TripRepository(),
         ),
+        // Group repository for managing travel groups
         RepositoryProvider<GroupRepository>(
           create: (context) => GroupRepository(),
         ),
+        // Message repository for handling in-app messaging
         RepositoryProvider<MessageRepository>(
           create: (context) => MessageRepository(),
         ),
+        // Account repository for managing user account settings
         RepositoryProvider<AccountRepository>(
           create: (context) => AccountRepository(),
         ),
+        // Expense repository for managing trip expenses
         RepositoryProvider<ExpenseRepository>(
           create: (context) => ExpenseRepository(),
         ),
-        // Provide service instances so BLoCs can read them with context.read<T>()
+        // Expense service for business logic related to expenses
         RepositoryProvider<ExpenseService>(
           create: (context) => ExpenseService(
             expenseRepository: context.read<ExpenseRepository>(),
           ),
         ),
+        // Balance repository for calculating expense balances
         RepositoryProvider<BalanceRepository>(
           create: (context) => BalanceRepository(
             expenseRepository: context.read<ExpenseRepository>(),
           ),
         ),
+        // Balance service for business logic related to balances
         RepositoryProvider<BalanceService>(
           create: (context) => BalanceService(
             balanceRepository: context.read<BalanceRepository>(),
@@ -87,38 +109,46 @@ class MyApp extends StatelessWidget {
       ],
       child: MultiBlocProvider(
         providers: [
+          // Theme BLoC for managing app theme preferences
           BlocProvider<ThemeBloc>(
             create: (context) => ThemeBloc()..add(ThemeLoadRequested()),
           ),
+          // Authentication BLoC for managing user authentication state
           BlocProvider<AuthBloc>(
             create: (context) =>
                 AuthBloc(authRepository: context.read<AuthRepository>())
                   ..add(AuthCheckRequested()),
           ),
+          // Group BLoC for managing travel groups
           BlocProvider(
             create: (context) => GroupBloc(context.read<GroupRepository>()),
           ),
+          // Trip BLoC for managing travel trips
           BlocProvider(
             create: (context) =>
                 TripBloc(context.read<TripRepository>()),
           ),
+          // User BLoC for managing user data
           BlocProvider(create: (context) => UserBloc()),
+          // Message BLoC for managing in-app messaging
           BlocProvider(
             create: (context) => MessageBloc(),
           ),
+          // Account BLoC for managing user account settings
           BlocProvider(
             create: (context) => AccountBloc(
               context.read<AccountRepository>(),
             ),
           ),
           
-          // Nouveaux blocs
+          // Expense BLoC for managing trip expenses
           BlocProvider<ExpenseBloc>(
             create: (context) => ExpenseBloc(
               expenseRepository: context.read<ExpenseRepository>(),
               expenseService: context.read<ExpenseService>(),
             ),
           ),
+          // Balance BLoC for managing expense balances and calculations
           BlocProvider<BalanceBloc>(
             create: (context) => BalanceBloc(
               balanceRepository: context.read<BalanceRepository>(),
@@ -134,6 +164,7 @@ class MyApp extends StatelessWidget {
               title: 'Travel Mate',
               navigatorKey: ErrorService.navigatorKey,
               themeMode: themeState.themeMode,
+              // Light theme configuration
               theme: ThemeData(
                 colorScheme: ColorScheme.fromSeed(
                   seedColor: const Color.fromARGB(255, 180, 180, 180),
@@ -141,6 +172,7 @@ class MyApp extends StatelessWidget {
                 ),
                 useMaterial3: true,
               ),
+              // Dark theme configuration
               darkTheme: ThemeData(
                 colorScheme: ColorScheme.fromSeed(
                   seedColor: const Color.fromARGB(255, 43, 43, 43),
@@ -148,7 +180,9 @@ class MyApp extends StatelessWidget {
                 ),
                 useMaterial3: true,
               ),
+              // Default page when app starts
               home: const LoginPage(),
+              // Named routes for navigation
               routes: {
                 '/login': (context) => const LoginPage(),
                 '/signup': (context) => const SignUpPage(),