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/repositories/product_repository.dart

@@ -3,6 +3,7 @@ import 'dart:developer';
 import 'package:dartz/dartz.dart';
 import 'package:injectable/injectable.dart';
 
+import '../../../common/service/unit_registry.dart';
 import '../../../domain/product/product.dart';
 import '../datasources/local_data_provider.dart';
 import '../datasources/remote_data_provider.dart';
@@ -12,10 +13,38 @@ import '../product_dtos.dart';
 class ProductRepository implements IProductRepository {
   final ProductRemoteDataProvider _remoteDataProvider;
   final ProductLocalDataProvider _localDataProvider;
+  final UnitRegistry _unitRegistry;
 
   final _logName = 'ProductRepository';
 
-  ProductRepository(this._remoteDataProvider, this._localDataProvider);
+  ProductRepository(
+    this._remoteDataProvider,
+    this._localDataProvider,
+    this._unitRegistry,
+  );
+
+  /// Response produk hanya dijamin membawa `unit_id`. Lengkapi nama dan
+  /// singkatannya dari master satuan supaya keranjang bisa menulis "4,2 ons".
+  Product _withUnit(Product product) {
+    if (!product.isSoldByWeight || product.unitId.isEmpty) return product;
+    if (product.unitAbbreviation.isNotEmpty && product.unitName.isNotEmpty) {
+      return product;
+    }
+
+    final unit = _unitRegistry.byId(product.unitId);
+    if (unit == null) return product;
+
+    return product.copyWith(
+      unitName: product.unitName.isNotEmpty ? product.unitName : unit.name,
+      unitAbbreviation: product.unitAbbreviation.isNotEmpty
+          ? product.unitAbbreviation
+          : unit.abbreviation,
+    );
+  }
+
+  List<Product> _withUnits(List<Product> products) =>
+      products.map(_withUnit).toList();
+
 
   @override
   Future<Either<ProductFailure, Product>> getProductById(String id) async {
@@ -33,7 +62,7 @@ class ProductRepository implements IProductRepository {
         );
       }
 
-      final productDomain = product.data!.toDomain();
+      final productDomain = _withUnit(product.data!.toDomain());
 
       log('✅ Product loaded: ${productDomain.name}', name: _logName);
       return Right(productDomain);
@@ -85,7 +114,9 @@ class ProductRepository implements IProductRepository {
 
       // 🧱 Bangun entity domain ListProduct
       final result = ListProduct(
-        products: cachedProducts.data!.map((p) => p.toDomain()).toList(),
+        products: _withUnits(
+          cachedProducts.data!.map((p) => p.toDomain()).toList(),
+        ),
         totalCount: totalCount,
         page: page,
         limit: limit,
@@ -132,7 +163,9 @@ class ProductRepository implements IProductRepository {
         return left(cachedProducts.error!);
       }
 
-      final products = cachedProducts.data!.map((p) => p.toDomain()).toList();
+      final products = _withUnits(
+        cachedProducts.data!.map((p) => p.toDomain()).toList(),
+      );
 
       final totalCount = await _localDataProvider.getTotalCount(
         categoryId: categoryId,
@@ -180,7 +213,9 @@ class ProductRepository implements IProductRepository {
       }
 
       // ✅ Mapping ke domain entity (kalau hasilnya masih berupa DTO)
-      final products = results.data!.map((p) => p.toDomain()).toList();
+      final products = _withUnits(
+        results.data!.map((p) => p.toDomain()).toList(),
+      );
 
       log(
         '✅ Local search completed: ${products.length} results',
@@ -369,7 +404,7 @@ class ProductRepository implements IProductRepository {
 
       final products = result.data!.toDomain();
 
-      return right(products);
+      return right(products.copyWith(products: _withUnits(products.products)));
     } catch (e, s) {
       log('getProducts', name: _logName, error: e, stackTrace: s);
       return left(const ProductFailure.unexpectedError());