feat: Implement account management functionality with loading, creation, and error handling

lib/data/models/account.dart

@@ -4,12 +4,14 @@ class Account {
   final String id;
   final String tripId;
   final String groupId;
+  final String name;
   final List<GroupMember> members;
 
   Account({
     required this.id,
     required this.tripId,
     required this.groupId,
+    required this.name,
     List<GroupMember>? members,
   }) : members = members ?? [];
 
@@ -19,6 +21,7 @@ class Account {
       id: map['id'] as String,
       tripId: map['tripId'] as String,
       groupId: map['groupId'] as String,
+      name: map['name'] as String,
       members: [],
     );
   }
@@ -28,6 +31,7 @@ class Account {
       'id': id,
       'tripId': tripId,
       'groupId': groupId,
+      'name': name,
       'members': members.map((member) => member.toMap()).toList(),
     };
   }
@@ -36,12 +40,14 @@ class Account {
     String? id,
     String? tripId,
     String? groupId,
+    String? name,
     List<GroupMember>? members,
   }) {
     return Account(
       id: id ?? this.id,
       tripId: tripId ?? this.tripId,
       groupId: groupId ?? this.groupId,
+      name: name ?? this.name,
       members: members ?? this.members,
     );
   }