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>

backend/internal/domain/userproduct/handler.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net/http"
 
+	"github.com/food-ai/backend/internal/domain/product"
 	"github.com/food-ai/backend/internal/infra/middleware"
 	"github.com/go-chi/chi/v5"
 )
@@ -18,16 +19,24 @@ type UserProductRepository interface {
 	BatchCreate(ctx context.Context, userID string, items []CreateRequest) ([]*UserProduct, error)
 	Update(ctx context.Context, id, userID string, req UpdateRequest) (*UserProduct, error)
 	Delete(ctx context.Context, id, userID string) error
+	DeleteAll(ctx context.Context, userID string) error
+}
+
+// ProductUpserter creates or updates a catalog product entry.
+// Implemented by product.Repository — defined here to avoid import cycles.
+type ProductUpserter interface {
+	Upsert(ctx context.Context, catalogProduct *product.Product) (*product.Product, error)
 }
 
 // Handler handles /user-products HTTP requests.
 type Handler struct {
-	repo UserProductRepository
+	repo            UserProductRepository
+	productUpserter ProductUpserter
 }
 
 // NewHandler creates a new Handler.
-func NewHandler(repo UserProductRepository) *Handler {
-	return &Handler{repo: repo}
+func NewHandler(repo UserProductRepository, productUpserter ProductUpserter) *Handler {
+	return &Handler{repo: repo, productUpserter: productUpserter}
 }
 
 // List handles GET /user-products.
@@ -47,7 +56,8 @@ func (handler *Handler) List(responseWriter http.ResponseWriter, request *http.R
 
 // Create handles POST /user-products.
 func (handler *Handler) Create(responseWriter http.ResponseWriter, request *http.Request) {
-	userID := middleware.UserIDFromCtx(request.Context())
+	requestContext := request.Context()
+	userID := middleware.UserIDFromCtx(requestContext)
 	var req CreateRequest
 	if decodeError := json.NewDecoder(request.Body).Decode(&req); decodeError != nil {
 		writeErrorJSON(responseWriter, request, http.StatusBadRequest, "invalid request body")
@@ -58,9 +68,40 @@ func (handler *Handler) Create(responseWriter http.ResponseWriter, request *http
 		return
 	}
 
-	userProduct, createError := handler.repo.Create(request.Context(), userID, req)
+	// Resolve effective primary_product_id (accept legacy mapping_id alias).
+	primaryProductID := req.PrimaryProductID
+	if primaryProductID == nil {
+		primaryProductID = req.MappingID
+	}
+
+	// When nutrition data is provided without an existing catalog link, upsert a catalog
+	// product so the nutrition info is not silently discarded.
+	hasNutrition := req.CaloriesPer100g != nil || req.ProteinPer100g != nil ||
+		req.FatPer100g != nil || req.CarbsPer100g != nil || req.FiberPer100g != nil
+	if hasNutrition && primaryProductID == nil {
+		catalogProduct := &product.Product{
+			CanonicalName:   req.Name,
+			Category:        req.Category,
+			DefaultUnit:     &req.Unit,
+			CaloriesPer100g: req.CaloriesPer100g,
+			ProteinPer100g:  req.ProteinPer100g,
+			FatPer100g:      req.FatPer100g,
+			CarbsPer100g:    req.CarbsPer100g,
+			FiberPer100g:    req.FiberPer100g,
+			StorageDays:     &req.StorageDays,
+		}
+		savedProduct, upsertError := handler.productUpserter.Upsert(requestContext, catalogProduct)
+		if upsertError != nil {
+			slog.WarnContext(requestContext, "upsert catalog product on manual add", "name", req.Name, "err", upsertError)
+			// Graceful degradation: continue without catalog link.
+		} else {
+			req.PrimaryProductID = &savedProduct.ID
+		}
+	}
+
+	userProduct, createError := handler.repo.Create(requestContext, userID, req)
 	if createError != nil {
-		slog.ErrorContext(request.Context(), "create user product", "user_id", userID, "err", createError)
+		slog.ErrorContext(requestContext, "create user product", "user_id", userID, "err", createError)
 		writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to create user product")
 		return
 	}
@@ -113,6 +154,17 @@ func (handler *Handler) Update(responseWriter http.ResponseWriter, request *http
 	writeJSON(responseWriter, http.StatusOK, userProduct)
 }
 
+// DeleteAll handles DELETE /user-products.
+func (handler *Handler) DeleteAll(responseWriter http.ResponseWriter, request *http.Request) {
+	userID := middleware.UserIDFromCtx(request.Context())
+	if deleteError := handler.repo.DeleteAll(request.Context(), userID); deleteError != nil {
+		slog.ErrorContext(request.Context(), "delete all user products", "user_id", userID, "err", deleteError)
+		writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to delete all user products")
+		return
+	}
+	responseWriter.WriteHeader(http.StatusNoContent)
+}
+
 // Delete handles DELETE /user-products/{id}.
 func (handler *Handler) Delete(responseWriter http.ResponseWriter, request *http.Request) {
 	userID := middleware.UserIDFromCtx(request.Context())