update cart

lib/features/products/domain/entities/product.dart

@@ -9,6 +9,27 @@ library;
 /// Represents a tile/construction product in the application.
 /// Used across all layers but originates in the domain layer.
 class Product {
+
+  const Product({
+    required this.productId,
+    required this.name,
+    this.description,
+    required this.basePrice,
+    required this.images,
+    required this.thumbnail,
+    required this.imageCaptions,
+    this.customLink360,
+    required this.specifications,
+    this.category,
+    this.brand,
+    this.unit,
+    this.conversionOfSm,
+    required this.isActive,
+    required this.isFeatured,
+    this.erpnextItemCode,
+    required this.createdAt,
+    required this.updatedAt,
+  });
   /// Unique identifier
   final String productId;
 
@@ -25,7 +46,7 @@ class Product {
   final List<String> images;
 
   /// Thumbnail image URL
-  final String? thumbnail;
+  final String thumbnail;
 
   /// Image captions
   final Map<String, String> imageCaptions;
@@ -45,6 +66,10 @@ class Product {
   /// Unit of measurement (e.g., "m²", "viên", "hộp")
   final String? unit;
 
+  /// Conversion factor for Square Meter UOM (tiles per m²)
+  /// Used to calculate: Số viên = Số lượng × conversionOfSm
+  final double? conversionOfSm;
+
   /// Product is active
   final bool isActive;
 
@@ -60,26 +85,6 @@ class Product {
   /// Last updated date
   final DateTime updatedAt;
 
-  const Product({
-    required this.productId,
-    required this.name,
-    this.description,
-    required this.basePrice,
-    required this.images,
-    this.thumbnail,
-    required this.imageCaptions,
-    this.customLink360,
-    required this.specifications,
-    this.category,
-    this.brand,
-    this.unit,
-    required this.isActive,
-    required this.isFeatured,
-    this.erpnextItemCode,
-    required this.createdAt,
-    required this.updatedAt,
-  });
-
   /// Get primary image URL
   String? get primaryImage => images.isNotEmpty ? images.first : null;
 
@@ -134,6 +139,7 @@ class Product {
     String? category,
     String? brand,
     String? unit,
+    double? conversionOfSm,
     bool? isActive,
     bool? isFeatured,
     String? erpnextItemCode,
@@ -153,6 +159,7 @@ class Product {
       category: category ?? this.category,
       brand: brand ?? this.brand,
       unit: unit ?? this.unit,
+      conversionOfSm: conversionOfSm ?? this.conversionOfSm,
       isActive: isActive ?? this.isActive,
       isFeatured: isFeatured ?? this.isFeatured,
       erpnextItemCode: erpnextItemCode ?? this.erpnextItemCode,