feat: dukung penjualan produk per timbangan

Produk kini punya cara jual `unit` (cacah) atau `weight` (timbangan),
mengikuti kontrak backend di docs/integration-weight-based-products.md.

- tipe SellBy, domain/infrastructure unit baru, dan endpoint /api/v1/units
- dialog input berat saat produk timbangan ditambahkan ke keranjang
- tiap penimbangan jadi baris keranjang sendiri; total baris dihitung
  berat x harga satuan, sedangkan produk cacah tetap digabung
- request ke backend mengirim quantity 1 dan membawa berat
- migrasi DB v3: kolom sell_by, unit_id, unit_name, unit_abbreviation
  di tabel products supaya satuan tetap tampil saat offline
- tampilan keranjang, struk, split bill, void, dan refund memakai berat
- test/weight_based_products_test.dart menutup perilaku di atas (9 test)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/infrastructure/order/order_dtos.g.dart

@@ -113,6 +113,10 @@ _$OrderItemDtoImpl _$$OrderItemDtoImplFromJson(Map<String, dynamic> json) =>
       paidQuantity: (json['paid_quantity'] as num?)?.toInt(),
       categoryId: json['category_id'] as String?,
       categoryName: json['category_name'] as String?,
+      weight: (json['weight'] as num?)?.toDouble(),
+      unitId: json['unit_id'] as String?,
+      unitName: json['unit_name'] as String?,
+      unitAbbreviation: json['unit_abbreviation'] as String?,
     );
 
 Map<String, dynamic> _$$OrderItemDtoImplToJson(_$OrderItemDtoImpl instance) =>
@@ -136,6 +140,10 @@ Map<String, dynamic> _$$OrderItemDtoImplToJson(_$OrderItemDtoImpl instance) =>
       'paid_quantity': instance.paidQuantity,
       'category_id': instance.categoryId,
       'category_name': instance.categoryName,
+      'weight': instance.weight,
+      'unit_id': instance.unitId,
+      'unit_name': instance.unitName,
+      'unit_abbreviation': instance.unitAbbreviation,
     };
 
 _$OrderRequestDtoImpl _$$OrderRequestDtoImplFromJson(
@@ -174,6 +182,7 @@ _$OrderItemRequestDtoImpl _$$OrderItemRequestDtoImplFromJson(
   quantity: (json['quantity'] as num?)?.toInt(),
   unitPrice: (json['unit_price'] as num?)?.toInt(),
   notes: json['notes'] as String?,
+  weight: (json['weight'] as num?)?.toDouble(),
 );
 
 Map<String, dynamic> _$$OrderItemRequestDtoImplToJson(
@@ -184,6 +193,7 @@ Map<String, dynamic> _$$OrderItemRequestDtoImplToJson(
   'quantity': instance.quantity,
   'unit_price': instance.unitPrice,
   'notes': instance.notes,
+  'weight': instance.weight,
 };
 
 _$PaymentRequestDtoImpl _$$PaymentRequestDtoImplFromJson(
@@ -317,6 +327,7 @@ _$AddItemOrderRequestDtoImpl _$$AddItemOrderRequestDtoImplFromJson(
   quantity: (json['quantity'] as num?)?.toInt(),
   unitPrice: (json['unit_price'] as num?)?.toInt(),
   notes: json['notes'] as String?,
+  weight: (json['weight'] as num?)?.toDouble(),
 );
 
 Map<String, dynamic> _$$AddItemOrderRequestDtoImplToJson(
@@ -327,4 +338,5 @@ Map<String, dynamic> _$$AddItemOrderRequestDtoImplToJson(
   'quantity': instance.quantity,
   'unit_price': instance.unitPrice,
   'notes': instance.notes,
+  'weight': instance.weight,
 };