fix: fix menu generation errors and show planned meals on home screen

Backend fixes:
- migration 003: add 'menu' value to recipe_source enum (was causing SQLSTATE 22P02)
- migration 004: rename recipe_products→recipe_ingredients, product_id→ingredient_id (was causing SQLSTATE 42P01)
- dish/repository.go: fix INSERT INTO tags using $1/$1 for two columns → $1/$2 (was causing SQLSTATE 42P08)
- home/handler.go: replace non-existent saved_recipes table with correct joins (recipes→dishes→dish_translations, user_saved_recipes) so today's plan and recommendations load correctly
- reqlog: new slog.Handler wrapper that adds request_id and stack trace to ERROR-level logs
- all handlers: slog.Error→slog.ErrorContext so error logs include request context; writeError includes request_id in response body

Client:
- home_screen.dart: extend home screen to future dates, show planned meals as ghost entries
- l10n: add new localisation keys for home screen date navigation and planned meal UI

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

backend/internal/domain/recommendation/handler.go

@@ -62,7 +62,7 @@ func NewHandler(recipeGenerator RecipeGenerator, pexels PhotoSearcher, userLoade
 func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.UserIDFromCtx(r.Context())
 	if userID == "" {
-		writeErrorJSON(w, http.StatusUnauthorized, "unauthorized")
+		writeErrorJSON(w, r, http.StatusUnauthorized, "unauthorized")
 		return
 	}
 
@@ -75,8 +75,8 @@ func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
 
 	u, err := h.userLoader.GetByID(r.Context(), userID)
 	if err != nil {
-		slog.Error("load user for recommendations", "user_id", userID, "err", err)
-		writeErrorJSON(w, http.StatusInternalServerError, "failed to load user profile")
+		slog.ErrorContext(r.Context(), "load user for recommendations", "user_id", userID, "err", err)
+		writeErrorJSON(w, r, http.StatusInternalServerError, "failed to load user profile")
 		return
 	}
 
@@ -86,13 +86,13 @@ func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
 	if products, err := h.productLister.ListForPrompt(r.Context(), userID); err == nil {
 		req.AvailableProducts = products
 	} else {
-		slog.Warn("load products for recommendations", "user_id", userID, "err", err)
+		slog.WarnContext(r.Context(), "load products for recommendations", "user_id", userID, "err", err)
 	}
 
 	recipes, err := h.recipeGenerator.GenerateRecipes(r.Context(), req)
 	if err != nil {
-		slog.Error("generate recipes", "user_id", userID, "err", err)
-		writeErrorJSON(w, http.StatusServiceUnavailable, "recipe generation failed, please try again")
+		slog.ErrorContext(r.Context(), "generate recipes", "user_id", userID, "err", err)
+		writeErrorJSON(w, r, http.StatusServiceUnavailable, "recipe generation failed, please try again")
 		return
 	}
 
@@ -104,7 +104,7 @@ func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
 			defer wg.Done()
 			imageURL, err := h.pexels.SearchPhoto(r.Context(), recipes[i].ImageQuery)
 			if err != nil {
-				slog.Warn("pexels photo search failed", "query", recipes[i].ImageQuery, "err", err)
+				slog.WarnContext(r.Context(), "pexels photo search failed", "query", recipes[i].ImageQuery, "err", err)
 			}
 			recipes[i].ImageURL = imageURL
 		}(i)
@@ -139,14 +139,18 @@ func buildRecipeRequest(u *user.User, count int, lang string) ai.RecipeRequest {
 }
 
 type errorResponse struct {
-	Error string `json:"error"`
+	Error     string `json:"error"`
+	RequestID string `json:"request_id,omitempty"`
 }
 
-func writeErrorJSON(w http.ResponseWriter, status int, msg string) {
+func writeErrorJSON(w http.ResponseWriter, r *http.Request, status int, msg string) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	if err := json.NewEncoder(w).Encode(errorResponse{Error: msg}); err != nil {
-		slog.Error("write error response", "err", err)
+	if encodeErr := json.NewEncoder(w).Encode(errorResponse{
+		Error:     msg,
+		RequestID: middleware.RequestIDFromCtx(r.Context()),
+	}); encodeErr != nil {
+		slog.ErrorContext(r.Context(), "write error response", "err", encodeErr)
 	}
 }