added createdAt timestamp to Group, Game, and Player DTOs

lib/data/dto/game.dart

@@ -8,14 +8,17 @@ class Game {
   final List<Player>? players;
   final Group? group;
   final String winner;
+  final DateTime createdAt;
 
   Game({
     String? id,
+    DateTime? createdAt,
     required this.name,
     this.players,
     this.group,
     this.winner = '',
-  }) : id = id ?? const Uuid().v4();
+  }) : id = id ?? const Uuid().v4(),
+       createdAt = createdAt ?? DateTime.now();
 
   @override
   String toString() {

lib/data/dto/group.dart

@@ -5,9 +5,15 @@ class Group {
   final String id;
   final String name;
   final List<Player> members;
+  final DateTime createdAt;
 
-  Group({String? id, required this.name, required this.members})
-    : id = id ?? const Uuid().v4();
+  Group({
+    String? id,
+    DateTime? createdAt,
+    required this.name,
+    required this.members,
+  }) : id = id ?? const Uuid().v4(),
+       createdAt = createdAt ?? DateTime.now();
 
   @override
   String toString() {

lib/data/dto/player.dart

@@ -3,8 +3,11 @@ import 'package:uuid/uuid.dart';
 class Player {
   final String id;
   final String name;
+  final DateTime createdAt;
 
-  Player({String? id, required this.name}) : id = id ?? const Uuid().v4();
+  Player({String? id, DateTime? createdAt, required this.name})
+    : id = id ?? const Uuid().v4(),
+      createdAt = createdAt ?? DateTime.now();
 
   @override
   String toString() {