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_ar.arb

@@ -172,5 +172,32 @@
   "jobTypeReceipt": "إيصال",
   "jobTypeProducts": "منتجات",
   "scanSubmitting": "جارٍ الإرسال...",
-  "processingProducts": "جارٍ المعالجة..."
+  "processingProducts": "جارٍ المعالجة...",
+  "clearAllProducts": "مسح الكل",
+  "clearAllConfirmTitle": "مسح جميع المنتجات؟",
+  "clearAllConfirmMessage": "سيتم حذف جميع المنتجات نهائياً.",
+  "addManually": "يدويًا",
+  "scan": "مسح ضوئي",
+  "addProduct": "إضافة",
+  "searchProducts": "البحث عن المنتجات",
+  "searchProductsHint": "اكتب اسم المنتج أو أضف يدويًا",
+  "noSearchResults": "لا توجد نتائج لـ\"{query}\"",
+  "@noSearchResults": {
+    "placeholders": {
+      "query": {
+        "type": "String"
+      }
+    }
+  },
+  "quantity": "الكمية",
+  "storageDays": "أيام التخزين",
+  "addToShelf": "إضافة إلى المخزن",
+  "errorGeneric": "حدث خطأ ما",
+  "nutritionOptional": "القيم الغذائية لكل 100 جم (اختياري)",
+  "calories": "سعرات حرارية",
+  "protein": "بروتين",
+  "fat": "دهون",
+  "carbs": "كربوهيدرات",
+  "fiber": "ألياف",
+  "productAddedToShelf": "تمت الإضافة إلى المخزن"
 }