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/units/handler.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 
 	"github.com/food-ai/backend/internal/infra/locale"
+	"github.com/food-ai/backend/internal/infra/middleware"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
@@ -26,8 +27,8 @@ func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
 			LEFT JOIN unit_translations ut ON ut.unit_code = u.code AND ut.lang = $1
 			ORDER BY u.sort_order`, lang)
 		if queryError != nil {
-			slog.Error("list units", "err", queryError)
-			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+			slog.ErrorContext(request.Context(), "list units", "err", queryError)
+			writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
 			return
 		}
 		defer rows.Close()
@@ -36,15 +37,15 @@ func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
 		for rows.Next() {
 			var item unitItem
 			if scanError := rows.Scan(&item.Code, &item.Name); scanError != nil {
-				slog.Error("scan unit row", "err", scanError)
-				writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+				slog.ErrorContext(request.Context(), "scan unit row", "err", scanError)
+				writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
 				return
 			}
 			items = append(items, item)
 		}
 		if rowsError := rows.Err(); rowsError != nil {
-			slog.Error("iterate unit rows", "err", rowsError)
-			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load units")
+			slog.ErrorContext(request.Context(), "iterate unit rows", "err", rowsError)
+			writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
 			return
 		}
 
@@ -53,8 +54,8 @@ func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
 	}
 }
 
-func writeErrorJSON(responseWriter http.ResponseWriter, status int, message string) {
+func writeErrorJSON(responseWriter http.ResponseWriter, request *http.Request, status int, msg string) {
 	responseWriter.Header().Set("Content-Type", "application/json")
 	responseWriter.WriteHeader(status)
-	_ = json.NewEncoder(responseWriter).Encode(map[string]string{"error": message})
+	_ = json.NewEncoder(responseWriter).Encode(map[string]any{"error": msg, "request_id": middleware.RequestIDFromCtx(request.Context())})
 }