feat: Add User and UserBalance models with serialization methods

feat: Implement BalanceRepository for group balance calculations

feat: Create ExpenseRepository for managing expenses

feat: Add services for handling expenses and storage operations

fix: Update import paths for models in repositories and services

refactor: Rename CountContent to AccountContent in HomePage

chore: Add StorageService for image upload and management

lib/components/account/balances_tab.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
-import '../../data/models/balance.dart';
+import '../../models/user_balance.dart';
 
 class BalancesTab extends StatelessWidget {
-  final List<Balance> balances;
+  final List<UserBalance> balances;
 
   const BalancesTab({
     super.key,
@@ -27,7 +27,7 @@ class BalancesTab extends StatelessWidget {
     );
   }
 
-  Widget _buildBalanceCard(BuildContext context, Balance balance) {
+  Widget _buildBalanceCard(BuildContext context, UserBalance balance) {
     final isDark = Theme.of(context).brightness == Brightness.dark;
     
     Color balanceColor;