refactor: introduce internal/domain/ layer, rename model.go → entity.go

Move all business-logic packages from internal/ root into internal/domain/:
  auth, cuisine, diary, dish, home, ingredient, language, menu, product,
  recipe, recognition, recommendation, savedrecipe, tag, units, user

Rename model.go → entity.go in packages that hold domain entities:
  diary, dish, home, ingredient, menu, product, recipe, savedrecipe, user

Update all import paths accordingly (adapters, infra/server, cmd/server,
tests). No logic changes.

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

backend/internal/domain/cuisine/handler.go

@@ -0,0 +1,60 @@
+package cuisine
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"github.com/food-ai/backend/internal/infra/locale"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+type cuisineItem struct {
+	Slug string `json:"slug"`
+	Name string `json:"name"`
+}
+
+// NewListHandler returns an http.HandlerFunc for GET /cuisines.
+// It queries the database directly, resolving translations via COALESCE.
+func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
+	return func(responseWriter http.ResponseWriter, request *http.Request) {
+		lang := locale.FromContext(request.Context())
+
+		rows, queryError := pool.Query(request.Context(), `
+			SELECT c.slug, COALESCE(ct.name, c.name) AS name
+			FROM cuisines c
+			LEFT JOIN cuisine_translations ct ON ct.cuisine_slug = c.slug AND ct.lang = $1
+			ORDER BY c.sort_order`, lang)
+		if queryError != nil {
+			slog.Error("list cuisines", "err", queryError)
+			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load cuisines")
+			return
+		}
+		defer rows.Close()
+
+		items := make([]cuisineItem, 0)
+		for rows.Next() {
+			var item cuisineItem
+			if scanError := rows.Scan(&item.Slug, &item.Name); scanError != nil {
+				slog.Error("scan cuisine row", "err", scanError)
+				writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load cuisines")
+				return
+			}
+			items = append(items, item)
+		}
+		if rowsError := rows.Err(); rowsError != nil {
+			slog.Error("iterate cuisine rows", "err", rowsError)
+			writeErrorJSON(responseWriter, http.StatusInternalServerError, "failed to load cuisines")
+			return
+		}
+
+		responseWriter.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(responseWriter).Encode(map[string]any{"cuisines": items})
+	}
+}
+
+func writeErrorJSON(responseWriter http.ResponseWriter, status int, message string) {
+	responseWriter.Header().Set("Content-Type", "application/json")
+	responseWriter.WriteHeader(status)
+	_ = json.NewEncoder(responseWriter).Encode(map[string]string{"error": message})
+}