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/product/product_dtos.g.dart

@@ -27,6 +27,21 @@ Map<String, dynamic> _$$ListProductDtoImplToJson(
   'total_pages': instance.totalPages,
 };
 
+_$ProductUnitDtoImpl _$$ProductUnitDtoImplFromJson(Map<String, dynamic> json) =>
+    _$ProductUnitDtoImpl(
+      id: json['id'] as String?,
+      name: json['name'] as String?,
+      abbreviation: json['abbreviation'] as String?,
+    );
+
+Map<String, dynamic> _$$ProductUnitDtoImplToJson(
+  _$ProductUnitDtoImpl instance,
+) => <String, dynamic>{
+  'id': instance.id,
+  'name': instance.name,
+  'abbreviation': instance.abbreviation,
+};
+
 _$ProductDtoImpl _$$ProductDtoImplFromJson(Map<String, dynamic> json) =>
     _$ProductDtoImpl(
       id: json['id'] as String?,
@@ -48,6 +63,13 @@ _$ProductDtoImpl _$$ProductDtoImplFromJson(Map<String, dynamic> json) =>
       variants: (json['variants'] as List<dynamic>?)
           ?.map((e) => ProductVariantDto.fromJson(e as Map<String, dynamic>))
           .toList(),
+      sellBy: json['sell_by'] as String?,
+      unitId: json['unit_id'] as String?,
+      unitName: json['unit_name'] as String?,
+      unitAbbreviation: json['unit_abbreviation'] as String?,
+      unit: json['unit'] == null
+          ? null
+          : ProductUnitDto.fromJson(json['unit'] as Map<String, dynamic>),
     );
 
 Map<String, dynamic> _$$ProductDtoImplToJson(_$ProductDtoImpl instance) =>
@@ -69,6 +91,11 @@ Map<String, dynamic> _$$ProductDtoImplToJson(_$ProductDtoImpl instance) =>
       'created_at': instance.createdAt,
       'updated_at': instance.updatedAt,
       'variants': instance.variants,
+      'sell_by': instance.sellBy,
+      'unit_id': instance.unitId,
+      'unit_name': instance.unitName,
+      'unit_abbreviation': instance.unitAbbreviation,
+      'unit': instance.unit,
     };
 
 _$ProductVariantDtoImpl _$$ProductVariantDtoImplFromJson(