feat: Implement group balance and expense management with new navigation and data handling

lib/main.dart

@@ -66,11 +66,23 @@ class MyApp extends StatelessWidget {
         RepositoryProvider<ExpenseRepository>(
           create: (context) => ExpenseRepository(),
         ),
+        // Provide service instances so BLoCs can read them with context.read<T>()
+        RepositoryProvider<ExpenseService>(
+          create: (context) => ExpenseService(
+            expenseRepository: context.read<ExpenseRepository>(),
+          ),
+        ),
         RepositoryProvider<BalanceRepository>(
           create: (context) => BalanceRepository(
             expenseRepository: context.read<ExpenseRepository>(),
           ),
         ),
+        RepositoryProvider<BalanceService>(
+          create: (context) => BalanceService(
+            balanceRepository: context.read<BalanceRepository>(),
+            expenseRepository: context.read<ExpenseRepository>(),
+          ),
+        ),
         
       ],
       child: MultiBlocProvider(