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/diary/handler.go

@@ -0,0 +1,110 @@
+package diary
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"github.com/food-ai/backend/internal/infra/middleware"
+	"github.com/go-chi/chi/v5"
+)
+
+// Handler handles diary endpoints.
+type Handler struct {
+	repo *Repository
+}
+
+// NewHandler creates a new Handler.
+func NewHandler(repo *Repository) *Handler {
+	return &Handler{repo: repo}
+}
+
+// GetByDate handles GET /diary?date=YYYY-MM-DD
+func (h *Handler) GetByDate(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.UserIDFromCtx(r.Context())
+	if userID == "" {
+		writeError(w, http.StatusUnauthorized, "unauthorized")
+		return
+	}
+
+	date := r.URL.Query().Get("date")
+	if date == "" {
+		writeError(w, http.StatusBadRequest, "date query parameter required (YYYY-MM-DD)")
+		return
+	}
+
+	entries, err := h.repo.ListByDate(r.Context(), userID, date)
+	if err != nil {
+		slog.Error("list diary by date", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to load diary")
+		return
+	}
+	if entries == nil {
+		entries = []*Entry{}
+	}
+	writeJSON(w, http.StatusOK, entries)
+}
+
+// Create handles POST /diary
+func (h *Handler) Create(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.UserIDFromCtx(r.Context())
+	if userID == "" {
+		writeError(w, http.StatusUnauthorized, "unauthorized")
+		return
+	}
+
+	var req CreateRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+	if req.Date == "" || req.Name == "" || req.MealType == "" {
+		writeError(w, http.StatusBadRequest, "date, meal_type and name are required")
+		return
+	}
+
+	entry, err := h.repo.Create(r.Context(), userID, req)
+	if err != nil {
+		slog.Error("create diary entry", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to create diary entry")
+		return
+	}
+	writeJSON(w, http.StatusCreated, entry)
+}
+
+// Delete handles DELETE /diary/{id}
+func (h *Handler) Delete(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.UserIDFromCtx(r.Context())
+	if userID == "" {
+		writeError(w, http.StatusUnauthorized, "unauthorized")
+		return
+	}
+
+	id := chi.URLParam(r, "id")
+	if err := h.repo.Delete(r.Context(), id, userID); err != nil {
+		if err == ErrNotFound {
+			writeError(w, http.StatusNotFound, "diary entry not found")
+			return
+		}
+		slog.Error("delete diary entry", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to delete diary entry")
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+type errorResponse struct {
+	Error string `json:"error"`
+}
+
+func writeError(w http.ResponseWriter, status int, msg string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(errorResponse{Error: msg})
+}
+
+func writeJSON(w http.ResponseWriter, status int, v any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(v)
+}