third commit

lib/domain/entities/product.dart

@@ -51,6 +51,7 @@ class Product extends Equatable {
     this.imageUrl,
     this.unit = UnitOfMeasure.piece,
     this.gstRate = AppConstants.defaultGstRate,
+    this.hsnCode,
     this.brand,
     this.isActive = true,
   });
@@ -72,6 +73,11 @@ class Product extends Equatable {
   final String? imageUrl;
   final UnitOfMeasure unit;
   final double gstRate;
+
+  /// HSN/SAC code. Printed on the tax invoice — legally required on a GST
+  /// invoice above the turnover threshold. Blank when the catalogue omits it.
+  final String? hsnCode;
+
   final String? brand;
   final bool isActive;
 
@@ -124,6 +130,7 @@ class Product extends Equatable {
       imageUrl: imageUrl,
       unit: unit,
       gstRate: gstRate,
+      hsnCode: hsnCode,
       brand: brand,
       isActive: isActive ?? this.isActive,
     );