feat: Implement account management features

- Added ExpenseDetailDialog for displaying expense details and actions.
- Created ExpensesTab to list expenses for a group.
- Developed GroupExpensesPage to manage group expenses with tabs for expenses, balances, and settlements.
- Introduced SettlementsTab to show optimized repayment plans.
- Refactored create_trip_content.dart to remove CountBloc and related logic.
- Added Account model to manage user accounts and group members.
- Replaced CountRepository with AccountRepository for account-related operations.
- Removed CountService and CountRepository as part of the refactor.
- Updated main.dart and home.dart to integrate new account management components.

lib/data/models/account.dart

@@ -0,0 +1,48 @@
+import 'group_member.dart';
+
+class Account {
+  final String id;
+  final String tripId;
+  final String groupId;
+  final List<GroupMember> members;
+
+  Account({
+    required this.id,
+    required this.tripId,
+    required this.groupId,
+    List<GroupMember>? members,
+  }) : members = members ?? [];
+
+
+  factory Account.fromMap(Map<String, dynamic> map) {
+    return Account(
+      id: map['id'] as String,
+      tripId: map['tripId'] as String,
+      groupId: map['groupId'] as String,
+      members: [],
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    return {
+      'id': id,
+      'tripId': tripId,
+      'groupId': groupId,
+      'members': members.map((member) => member.toMap()).toList(),
+    };
+  }
+
+  Account copyWith({
+    String? id,
+    String? tripId,
+    String? groupId,
+    List<GroupMember>? members,
+  }) {
+    return Account(
+      id: id ?? this.id,
+      tripId: tripId ?? this.tripId,
+      groupId: groupId ?? this.groupId,
+      members: members ?? this.members,
+    );
+  }
+}