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/adapters/openai/recipe.go

@@ -16,7 +16,6 @@ var goalNames = map[string]string{
 	"gain":     "muscle gain",
 }
 
-
 // GenerateRecipes generates recipes using the OpenAI API.
 // Retries up to maxRetries times only when the response is not valid JSON.
 // API-level errors (rate limits, auth, etc.) are returned immediately.
@@ -62,11 +61,6 @@ func buildRecipePrompt(req ai.RecipeRequest) string {
 		goal = "weight maintenance"
 	}
 
-	targetLang := langNames[req.Lang]
-	if targetLang == "" {
-		targetLang = "English"
-	}
-
 	restrictions := "none"
 	if len(req.Restrictions) > 0 {
 		restrictions = strings.Join(req.Restrictions, ", ")
@@ -93,7 +87,7 @@ func buildRecipePrompt(req ai.RecipeRequest) string {
 			strings.Join(req.AvailableProducts, "\n") + "\n"
 	}
 
-	return fmt.Sprintf(`You are a chef and nutritionist. Generate %d recipes in %s.
+	return fmt.Sprintf(`You are a chef and nutritionist. Generate %d recipes in English.
 
 User profile:
 - Goal: %s
@@ -107,7 +101,7 @@ Requirements for each recipe:
 - Include approximate macros per serving
 
 IMPORTANT:
-- All text fields (title, description, ingredient names, units, step descriptions, tags) MUST be in %s.
+- All text fields (title, description, ingredient names, units, step descriptions, tags) MUST be in English.
 - The "image_query" field MUST always be in English (it is used for stock-photo search).
 
 Return ONLY a valid JSON array without markdown or extra text:
@@ -124,7 +118,7 @@ Return ONLY a valid JSON array without markdown or extra text:
   "steps": [{"number": 1, "description": "...", "timer_seconds": null}],
   "tags": ["..."],
   "nutrition_per_serving": {"calories": 420, "protein_g": 48, "fat_g": 12, "carbs_g": 18}
-}]`, count, targetLang, goal, req.DailyCalories, restrictions, cuisines, productsSection, perMealCalories, targetLang)
+}]`, count, goal, req.DailyCalories, restrictions, cuisines, productsSection, perMealCalories)
 }
 
 func parseRecipesJSON(text string) ([]ai.Recipe, error) {