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_ko.arb

@@ -172,5 +172,32 @@
   "jobTypeReceipt": "영수증",
   "jobTypeProducts": "제품",
   "scanSubmitting": "제출 중...",
-  "processingProducts": "처리 중..."
+  "processingProducts": "처리 중...",
+  "clearAllProducts": "모두 지우기",
+  "clearAllConfirmTitle": "모든 제품을 지울까요?",
+  "clearAllConfirmMessage": "모든 제품이 영구적으로 삭제됩니다.",
+  "addManually": "수동",
+  "scan": "스캔",
+  "addProduct": "추가",
+  "searchProducts": "제품 검색",
+  "searchProductsHint": "제품 이름을 입력하거나 수동으로 추가하세요",
+  "noSearchResults": "「{query}」에 대한 결과가 없습니다",
+  "@noSearchResults": {
+    "placeholders": {
+      "query": {
+        "type": "String"
+      }
+    }
+  },
+  "quantity": "수량",
+  "storageDays": "보관 일수",
+  "addToShelf": "저장실에 추가",
+  "errorGeneric": "오류가 발생했습니다",
+  "nutritionOptional": "100g당 영양성분 (선택사항)",
+  "calories": "칼로리",
+  "protein": "단백질",
+  "fat": "지방",
+  "carbs": "탄수화물",
+  "fiber": "식이섬유",
+  "productAddedToShelf": "저장실에 추가되었습니다"
 }