feat: translate recommendations and menu dishes into user language

- Generate recipes in English (reverted prompt to English-only)
- Add TranslateRecipes to OpenAI client (translate.go) — sends compact
  JSON payload of translatable fields, merges back into original recipes
- recommendation/handler.go: translate recipes in-memory before response
  when lang != "en"; falls back to English on error
- dish/repository.go: Create() now returns (dishID, recipeID, err) so
  callers can upsert dish_translations after saving
- menu/handler.go: saveRecipes returns savedRecipeEntry slice with dishID;
  saveDishTranslations calls TranslateRecipes then UpsertTranslation for
  each dish when the request locale is not English
- savedrecipe/repository.go: updated to ignore dishID from Create()
- init.go: wire openaiClient as RecipeTranslator and dishRepository as
  DishTranslator for menu.NewHandler

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

backend/internal/domain/recommendation/handler.go

@@ -40,18 +40,25 @@ type RecipeGenerator interface {
 	GenerateRecipes(ctx context.Context, req ai.RecipeRequest) ([]ai.Recipe, error)
 }
 
+// RecipeTranslator translates a slice of English recipes into a target language.
+type RecipeTranslator interface {
+	TranslateRecipes(ctx context.Context, recipes []ai.Recipe, targetLang string) ([]ai.Recipe, error)
+}
+
 // Handler handles GET /recommendations.
 type Handler struct {
 	recipeGenerator RecipeGenerator
+	translator      RecipeTranslator
 	pexels          PhotoSearcher
 	userLoader      UserLoader
 	productLister   ProductLister
 }
 
 // NewHandler creates a new Handler.
-func NewHandler(recipeGenerator RecipeGenerator, pexels PhotoSearcher, userLoader UserLoader, productLister ProductLister) *Handler {
+func NewHandler(recipeGenerator RecipeGenerator, translator RecipeTranslator, pexels PhotoSearcher, userLoader UserLoader, productLister ProductLister) *Handler {
 	return &Handler{
 		recipeGenerator: recipeGenerator,
+		translator:      translator,
 		pexels:          pexels,
 		userLoader:      userLoader,
 		productLister:   productLister,
@@ -111,6 +118,20 @@ func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
 	}
 	wg.Wait()
 
+	// Translate text fields into the requested language.
+	// The generation prompt always produces English; translations are applied
+	// in-memory here since recommendations are not persisted to the database.
+	lang := locale.FromContext(r.Context())
+	if lang != "en" {
+		translated, translateError := h.translator.TranslateRecipes(r.Context(), recipes, lang)
+		if translateError != nil {
+			slog.WarnContext(r.Context(), "translate recommendations", "lang", lang, "err", translateError)
+			// Fall back to English rather than failing the request.
+		} else {
+			recipes = translated
+		}
+	}
+
 	writeJSON(w, http.StatusOK, recipes)
 }