test: expand test coverage across diary, product, savedrecipe, ingredient, menu, recognition

- Fix locale_test: add TestMain to pre-populate Supported map so zh/es tests pass
- Export pure functions for testability: ResolveWeekStart, MapCuisineSlug (menu + savedrecipe), MergeAndDeduplicate
- Introduce repository interfaces (DiaryRepository, ProductRepository, SavedRecipeRepository, IngredientSearcher) in each handler; NewHandler now accepts interfaces — concrete *Repository still satisfies them
- Add mock files: diary/mocks, product/mocks, savedrecipe/mocks
- Add handler unit tests (no DB) for diary (8), product (8), savedrecipe (8), ingredient (5)
- Add pure-function unit tests: menu/ResolveWeekStart (6), savedrecipe/MapCuisineSlug (5), recognition/MergeAndDeduplicate (6)
- Add repository integration tests (//go:build integration): diary (4), product (6)
- Extend recipe integration tests: GetByID_Found, GetByID_WithTranslation

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

backend/tests/diary/repository_integration_test.go

@@ -0,0 +1,118 @@
+//go:build integration
+
+package diary_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/food-ai/backend/internal/domain/diary"
+	"github.com/food-ai/backend/internal/testutil"
+)
+
+func TestDiaryRepository_Create_Defaults(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := diary.NewRepository(pool)
+	requestContext := context.Background()
+
+	// portions=0 → repository sets 1; source="" → repository sets "manual"
+	entry, createError := repo.Create(requestContext, "test-user", diary.CreateRequest{
+		Date:     "2026-03-15",
+		MealType: "breakfast",
+		Name:     "Oatmeal",
+		Portions: 0,
+		Source:   "",
+	})
+	if createError != nil {
+		t.Fatalf("create diary entry: %v", createError)
+	}
+	if entry.Portions != 1 {
+		t.Errorf("expected portions=1, got %v", entry.Portions)
+	}
+	if entry.Source != "manual" {
+		t.Errorf("expected source=manual, got %q", entry.Source)
+	}
+}
+
+func TestDiaryRepository_ListByDate(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := diary.NewRepository(pool)
+	requestContext := context.Background()
+
+	userID := "list-date-user"
+	date := "2026-03-15"
+
+	_, createError := repo.Create(requestContext, userID, diary.CreateRequest{
+		Date: date, MealType: "breakfast", Name: "Oatmeal",
+	})
+	if createError != nil {
+		t.Fatalf("create first entry: %v", createError)
+	}
+	_, createError = repo.Create(requestContext, userID, diary.CreateRequest{
+		Date: date, MealType: "lunch", Name: "Salad",
+	})
+	if createError != nil {
+		t.Fatalf("create second entry: %v", createError)
+	}
+
+	entries, listError := repo.ListByDate(requestContext, userID, date)
+	if listError != nil {
+		t.Fatalf("list by date: %v", listError)
+	}
+	if len(entries) != 2 {
+		t.Errorf("expected 2 entries, got %d", len(entries))
+	}
+}
+
+func TestDiaryRepository_ListByDate_OtherUserNotReturned(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := diary.NewRepository(pool)
+	requestContext := context.Background()
+
+	date := "2026-03-15"
+
+	_, createError := repo.Create(requestContext, "user-A", diary.CreateRequest{
+		Date: date, MealType: "breakfast", Name: "Eggs",
+	})
+	if createError != nil {
+		t.Fatalf("create entry for user-A: %v", createError)
+	}
+
+	entries, listError := repo.ListByDate(requestContext, "user-B", date)
+	if listError != nil {
+		t.Fatalf("list by date for user-B: %v", listError)
+	}
+	if len(entries) != 0 {
+		t.Errorf("expected 0 entries for user-B, got %d", len(entries))
+	}
+}
+
+func TestDiaryRepository_Delete_NotFound(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := diary.NewRepository(pool)
+	requestContext := context.Background()
+
+	deleteError := repo.Delete(requestContext, "00000000-0000-0000-0000-000000000000", "any-user")
+	if deleteError != diary.ErrNotFound {
+		t.Errorf("expected ErrNotFound, got %v", deleteError)
+	}
+}
+
+func TestDiaryRepository_Delete_WrongUser(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := diary.NewRepository(pool)
+	requestContext := context.Background()
+
+	entry, createError := repo.Create(requestContext, "owner-user", diary.CreateRequest{
+		Date: "2026-03-15", MealType: "dinner", Name: "Pasta",
+	})
+	if createError != nil {
+		t.Fatalf("create entry: %v", createError)
+	}
+
+	// Attempt to delete another user's entry — should return ErrNotFound.
+	deleteError := repo.Delete(requestContext, entry.ID, "different-user")
+	if deleteError != diary.ErrNotFound {
+		t.Errorf("expected ErrNotFound when deleting another user's entry, got %v", deleteError)
+	}
+}