refactor: move all tests to backend/tests/ as black-box packages

All test files relocated from internal/X/ to tests/X/ and converted
to package X_test, using only the public API of each package.

- tests/auth/: jwt, service, handler integration tests
- tests/middleware/: auth, request_id, recovery tests
- tests/user/: calories, service, repository integration tests
- tests/locale/: locale tests (already package locale_test, just moved)
- tests/ingredient/: repository integration tests
- tests/recipe/: repository integration tests

mockUserRepo in tests/user/service_test.go redefined locally with
fully-qualified user.* types. Unexported auth.refreshRequest replaced
with a local testRefreshRequest struct in the integration test.

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

backend/tests/recipe/repository_integration_test.go

@@ -0,0 +1,36 @@
+//go:build integration
+
+package recipe_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/food-ai/backend/internal/recipe"
+	"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()
+
+	got, getError := repo.GetByID(ctx, "00000000-0000-0000-0000-000000000000")
+	if getError != nil {
+		t.Fatalf("unexpected error: %v", getError)
+	}
+	if got != nil {
+		t.Error("expected nil for non-existent ID")
+	}
+}
+
+func TestRecipeRepository_Count(t *testing.T) {
+	pool := testutil.SetupTestDB(t)
+	repo := recipe.NewRepository(pool)
+	ctx := context.Background()
+
+	_, countError := repo.Count(ctx)
+	if countError != nil {
+		t.Fatalf("count: %v", countError)
+	}
+}