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/recipe/repository_integration_test.go

@@ -6,16 +6,18 @@ import (
 	"context"
 	"testing"
 
+	"github.com/food-ai/backend/internal/domain/dish"
 	"github.com/food-ai/backend/internal/domain/recipe"
+	"github.com/food-ai/backend/internal/infra/locale"
 	"github.com/food-ai/backend/internal/testutil"
 )
 
 func TestRecipeRepository_GetByID_NotFound(t *testing.T) {
 	pool := testutil.SetupTestDB(t)
 	repo := recipe.NewRepository(pool)
-	ctx := context.Background()
+	requestContext := context.Background()
 
-	got, getError := repo.GetByID(ctx, "00000000-0000-0000-0000-000000000000")
+	got, getError := repo.GetByID(requestContext, "00000000-0000-0000-0000-000000000000")
 	if getError != nil {
 		t.Fatalf("unexpected error: %v", getError)
 	}
@@ -27,10 +29,92 @@ func TestRecipeRepository_GetByID_NotFound(t *testing.T) {
 func TestRecipeRepository_Count(t *testing.T) {
 	pool := testutil.SetupTestDB(t)
 	repo := recipe.NewRepository(pool)
-	ctx := context.Background()
+	requestContext := context.Background()
 
-	_, countError := repo.Count(ctx)
+	_, countError := repo.Count(requestContext)
 	if countError != nil {
 		t.Fatalf("count: %v", countError)
 	}
 }
+
+func TestRecipeRepository_GetByID_Found(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	dishRepo := dish.NewRepository(pool)
+	recipeRepo := recipe.NewRepository(pool)
+	requestContext := context.Background()
+
+	recipeID, createError := dishRepo.Create(requestContext, dish.CreateRequest{
+		Name:        "Test Pasta",
+		Description: "A simple pasta dish",
+		Source:      "test",
+		Ingredients: []dish.IngredientInput{
+			{Name: "pasta", Amount: 200, Unit: "g"},
+		},
+		Steps: []dish.StepInput{
+			{Number: 1, Description: "Boil water"},
+		},
+	})
+	if createError != nil {
+		t.Fatalf("create dish+recipe: %v", createError)
+	}
+
+	found, getError := recipeRepo.GetByID(requestContext, recipeID)
+	if getError != nil {
+		t.Fatalf("get recipe: %v", getError)
+	}
+	if found == nil {
+		t.Fatal("expected recipe to be found, got nil")
+	}
+	if found.ID != recipeID {
+		t.Errorf("expected ID %q, got %q", recipeID, found.ID)
+	}
+	if len(found.Ingredients) != 1 {
+		t.Errorf("expected 1 ingredient, got %d", len(found.Ingredients))
+	}
+	if found.Ingredients[0].Name != "pasta" {
+		t.Errorf("expected ingredient name 'pasta', got %q", found.Ingredients[0].Name)
+	}
+	if len(found.Steps) != 1 {
+		t.Errorf("expected 1 step, got %d", len(found.Steps))
+	}
+}
+
+func TestRecipeRepository_GetByID_WithTranslation(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	dishRepo := dish.NewRepository(pool)
+	recipeRepo := recipe.NewRepository(pool)
+	baseContext := context.Background()
+
+	recipeID, createError := dishRepo.Create(baseContext, dish.CreateRequest{
+		Name:        "Pasta Bolognese",
+		Description: "Classic Italian pasta",
+		Source:      "test",
+	})
+	if createError != nil {
+		t.Fatalf("create dish+recipe: %v", createError)
+	}
+
+	// Without translation context, the recipe should return English content.
+	enContext := locale.WithLang(baseContext, "en")
+	recipeEN, getError := recipeRepo.GetByID(enContext, recipeID)
+	if getError != nil {
+		t.Fatalf("get recipe (en): %v", getError)
+	}
+	if recipeEN == nil {
+		t.Fatal("expected recipe, got nil")
+	}
+
+	// With a language not having a translation, fallback to English should occur.
+	ruContext := locale.WithLang(baseContext, "ru")
+	recipeRU, getError := recipeRepo.GetByID(ruContext, recipeID)
+	if getError != nil {
+		t.Fatalf("get recipe (ru): %v", getError)
+	}
+	if recipeRU == nil {
+		t.Fatal("expected recipe with ru context, got nil")
+	}
+	// Both should refer to the same recipe ID.
+	if recipeEN.ID != recipeRU.ID {
+		t.Errorf("expected same recipe ID, got %q vs %q", recipeEN.ID, recipeRU.ID)
+	}
+}