feat: refactor code

lib/feature/auth/data/model/user_model.dart

@@ -0,0 +1,18 @@
+import '../../domain/entities/user_entity.dart';
+
+/// مدلِ داده‌ی کاربر؛ از JSON ساخته شده و به UserEntity نگاشت می‌شود.
+class UserModel extends UserEntity {
+  const UserModel({
+    required super.id,
+    required super.mobile,
+    super.firstName,
+    super.avatar,
+  });
+
+  factory UserModel.fromJson(Map<String, dynamic> j) => UserModel(
+        id: (j['id'] ?? 0) as int,
+        mobile: (j['mobile'] ?? '') as String,
+        firstName: j['first_name'] as String?,
+        avatar: j['avatar'] as String?,
+      );
+}