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/blocs/balance/balance_event.dart

@@ -0,0 +1,43 @@
+import 'package:equatable/equatable.dart';
+
+abstract class BalanceEvent extends Equatable {
+  const BalanceEvent();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class LoadGroupBalance extends BalanceEvent {
+  final String groupId;
+
+  const LoadGroupBalance(this.groupId);
+
+  @override
+  List<Object?> get props => [groupId];
+}
+
+class RefreshBalance extends BalanceEvent {
+  final String groupId;
+
+  const RefreshBalance(this.groupId);
+
+  @override
+  List<Object?> get props => [groupId];
+}
+
+class MarkSettlementAsCompleted extends BalanceEvent {
+  final String groupId;
+  final String fromUserId;
+  final String toUserId;
+  final double amount;
+
+  const MarkSettlementAsCompleted({
+    required this.groupId,
+    required this.fromUserId,
+    required this.toUserId,
+    required this.amount,
+  });
+
+  @override
+  List<Object?> get props => [groupId, fromUserId, toUserId, amount];
+}