feat: product search screen with catalog add and success feedback

- Add product search screen (/products/search) as primary add flow;
  "Add" button on products list opens search, manual entry remains as fallback
- Add to shelf bottom sheet with AnimatedSwitcher success view (green checkmark)
  and SnackBar confirmation on the search screen via onAdded callback
- Manual add (AddProductScreen) shows SnackBar on success before popping back
- Extend AddProductScreen with optional nutrition fields (calories, protein,
  fat, carbs, fiber); auto-fills from catalog selection and auto-expands section
- Auto-upsert catalog product on backend when nutrition data is provided
  without a primary_product_id, linking the user product to the catalog
- Add fiber_per_100g field to CatalogProduct model and CreateRequest
- Add 16 new L10n keys across all 12 locales (addProduct, addManually,
  searchProducts, quantity, storageDays, addToShelf, nutritionOptional,
  calories, protein, fat, carbs, fiber, productAddedToShelf, etc.)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/l10n/app_localizations_ko.dart

@@ -470,4 +470,66 @@ class AppLocalizationsKo extends AppLocalizations {
 
   @override
   String get processingProducts => '처리 중...';
+
+  @override
+  String get clearAllProducts => '모두 지우기';
+
+  @override
+  String get clearAllConfirmTitle => '모든 제품을 지울까요?';
+
+  @override
+  String get clearAllConfirmMessage => '모든 제품이 영구적으로 삭제됩니다.';
+
+  @override
+  String get addManually => '수동';
+
+  @override
+  String get scan => '스캔';
+
+  @override
+  String get addProduct => '추가';
+
+  @override
+  String get searchProducts => '제품 검색';
+
+  @override
+  String get searchProductsHint => '제품 이름을 입력하거나 수동으로 추가하세요';
+
+  @override
+  String noSearchResults(String query) {
+    return '「$query」에 대한 결과가 없습니다';
+  }
+
+  @override
+  String get quantity => '수량';
+
+  @override
+  String get storageDays => '보관 일수';
+
+  @override
+  String get addToShelf => '저장실에 추가';
+
+  @override
+  String get errorGeneric => '오류가 발생했습니다';
+
+  @override
+  String get nutritionOptional => '100g당 영양성분 (선택사항)';
+
+  @override
+  String get calories => '칼로리';
+
+  @override
+  String get protein => '단백질';
+
+  @override
+  String get fat => '지방';
+
+  @override
+  String get carbs => '탄수화물';
+
+  @override
+  String get fiber => '식이섬유';
+
+  @override
+  String get productAddedToShelf => '저장실에 추가되었습니다';
 }