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.dart

@@ -1029,6 +1029,126 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Processing...'**
   String get processingProducts;
+
+  /// No description provided for @clearAllProducts.
+  ///
+  /// In en, this message translates to:
+  /// **'Clear all'**
+  String get clearAllProducts;
+
+  /// No description provided for @clearAllConfirmTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Clear all products?'**
+  String get clearAllConfirmTitle;
+
+  /// No description provided for @clearAllConfirmMessage.
+  ///
+  /// In en, this message translates to:
+  /// **'All products will be permanently deleted.'**
+  String get clearAllConfirmMessage;
+
+  /// No description provided for @addManually.
+  ///
+  /// In en, this message translates to:
+  /// **'Manually'**
+  String get addManually;
+
+  /// No description provided for @scan.
+  ///
+  /// In en, this message translates to:
+  /// **'Scan'**
+  String get scan;
+
+  /// No description provided for @addProduct.
+  ///
+  /// In en, this message translates to:
+  /// **'Add'**
+  String get addProduct;
+
+  /// No description provided for @searchProducts.
+  ///
+  /// In en, this message translates to:
+  /// **'Search products'**
+  String get searchProducts;
+
+  /// No description provided for @searchProductsHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Type a product name to search or add manually'**
+  String get searchProductsHint;
+
+  /// No description provided for @noSearchResults.
+  ///
+  /// In en, this message translates to:
+  /// **'No results for \"{query}\"'**
+  String noSearchResults(String query);
+
+  /// No description provided for @quantity.
+  ///
+  /// In en, this message translates to:
+  /// **'Quantity'**
+  String get quantity;
+
+  /// No description provided for @storageDays.
+  ///
+  /// In en, this message translates to:
+  /// **'Storage days'**
+  String get storageDays;
+
+  /// No description provided for @addToShelf.
+  ///
+  /// In en, this message translates to:
+  /// **'Add to pantry'**
+  String get addToShelf;
+
+  /// No description provided for @errorGeneric.
+  ///
+  /// In en, this message translates to:
+  /// **'Something went wrong'**
+  String get errorGeneric;
+
+  /// No description provided for @nutritionOptional.
+  ///
+  /// In en, this message translates to:
+  /// **'Nutrition per 100g (optional)'**
+  String get nutritionOptional;
+
+  /// No description provided for @calories.
+  ///
+  /// In en, this message translates to:
+  /// **'Calories'**
+  String get calories;
+
+  /// No description provided for @protein.
+  ///
+  /// In en, this message translates to:
+  /// **'Protein'**
+  String get protein;
+
+  /// No description provided for @fat.
+  ///
+  /// In en, this message translates to:
+  /// **'Fat'**
+  String get fat;
+
+  /// No description provided for @carbs.
+  ///
+  /// In en, this message translates to:
+  /// **'Carbohydrates'**
+  String get carbs;
+
+  /// No description provided for @fiber.
+  ///
+  /// In en, this message translates to:
+  /// **'Fiber'**
+  String get fiber;
+
+  /// No description provided for @productAddedToShelf.
+  ///
+  /// In en, this message translates to:
+  /// **'Added to pantry'**
+  String get productAddedToShelf;
 }
 
 class _AppLocalizationsDelegate