add refresh token

lib/features/products/data/models/product_model.dart

@@ -31,10 +31,10 @@ class ProductModel extends HiveObject {
   final bool isAvailable;
 
   @HiveField(8)
-  final DateTime createdAt;
+  final DateTime? createdAt;
 
   @HiveField(9)
-  final DateTime updatedAt;
+  final DateTime? updatedAt;
 
   ProductModel({
     required this.id,
@@ -45,8 +45,8 @@ class ProductModel extends HiveObject {
     required this.categoryId,
     required this.stockQuantity,
     required this.isAvailable,
-    required this.createdAt,
-    required this.updatedAt,
+    this.createdAt,
+    this.updatedAt,
   });
 
   /// Convert to domain entity
@@ -92,8 +92,12 @@ class ProductModel extends HiveObject {
       categoryId: json['categoryId'] as String,
       stockQuantity: json['stockQuantity'] as int? ?? 0,
       isAvailable: json['isAvailable'] as bool? ?? true,
-      createdAt: DateTime.parse(json['createdAt'] as String),
-      updatedAt: DateTime.parse(json['updatedAt'] as String),
+      createdAt: json['createdAt'] != null
+          ? DateTime.parse(json['createdAt'] as String)
+          : null,
+      updatedAt: json['updatedAt'] != null
+          ? DateTime.parse(json['updatedAt'] as String)
+          : null,
     );
   }
 
@@ -108,8 +112,8 @@ class ProductModel extends HiveObject {
       'categoryId': categoryId,
       'stockQuantity': stockQuantity,
       'isAvailable': isAvailable,
-      'createdAt': createdAt.toIso8601String(),
-      'updatedAt': updatedAt.toIso8601String(),
+      'createdAt': createdAt?.toIso8601String(),
+      'updatedAt': updatedAt?.toIso8601String(),
     };
   }
 }

lib/features/products/data/models/product_model.g.dart

@@ -25,8 +25,8 @@ class ProductModelAdapter extends TypeAdapter<ProductModel> {
       categoryId: fields[5] as String,
       stockQuantity: (fields[6] as num).toInt(),
       isAvailable: fields[7] as bool,
-      createdAt: fields[8] as DateTime,
-      updatedAt: fields[9] as DateTime,
+      createdAt: fields[8] as DateTime?,
+      updatedAt: fields[9] as DateTime?,
     );
   }