feat: Implement group management with BLoC pattern; add GroupBloc, GroupRepository, and related models

NOT FUNCTIONNAL

lib/main.dart

@@ -13,6 +13,7 @@ import 'blocs/trip/trip_bloc.dart';
 import 'repositories/auth_repository.dart';
 import 'repositories/trip_repository.dart';
 import 'repositories/user_repository.dart';
+import 'repositories/group_repository.dart';
 import 'pages/login.dart';
 import 'pages/home.dart';
 import 'pages/signup.dart';
@@ -41,6 +42,9 @@ class MyApp extends StatelessWidget {
         RepositoryProvider<TripRepository>(
           create: (context) => TripRepository(),
         ),
+        RepositoryProvider<GroupRepository>(
+          create: (context) => GroupRepository(),
+        ),
       ],
       child: MultiBlocProvider(
         providers: [
@@ -52,7 +56,9 @@ class MyApp extends StatelessWidget {
               authRepository: context.read<AuthRepository>(),
             )..add(AuthCheckRequested()),
           ),
-          BlocProvider(create: (context) => GroupBloc()),
+          BlocProvider(create: (context) => GroupBloc(
+                context.read<GroupRepository>(),
+          )),
           BlocProvider(create: (context) => TripBloc(
                 tripRepository: context.read<TripRepository>(),
               ),