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/savedrecipe/map_cuisine_slug_test.go

@@ -0,0 +1,71 @@
+package savedrecipe_test
+
+import (
+	"testing"
+
+	"github.com/food-ai/backend/internal/domain/savedrecipe"
+)
+
+func TestMapCuisineSlug_KnownCuisines(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"italian", "italian"},
+		{"french", "french"},
+		{"russian", "russian"},
+		{"chinese", "chinese"},
+		{"japanese", "japanese"},
+		{"korean", "korean"},
+		{"mexican", "mexican"},
+		{"mediterranean", "mediterranean"},
+		{"indian", "indian"},
+		{"thai", "thai"},
+		{"american", "american"},
+		{"georgian", "georgian"},
+		{"spanish", "spanish"},
+		{"german", "german"},
+		{"middle_eastern", "middle_eastern"},
+		{"turkish", "turkish"},
+		{"greek", "greek"},
+		{"vietnamese", "vietnamese"},
+	}
+
+	for _, tc := range tests {
+		result := savedrecipe.MapCuisineSlug(tc.input)
+		if result != tc.want {
+			t.Errorf("MapCuisineSlug(%q) = %q, want %q", tc.input, result, tc.want)
+		}
+	}
+}
+
+func TestMapCuisineSlug_GenericFallsToOther(t *testing.T) {
+	for _, input := range []string{"asian", "european"} {
+		result := savedrecipe.MapCuisineSlug(input)
+		if result != "other" {
+			t.Errorf("MapCuisineSlug(%q) = %q, want %q", input, result, "other")
+		}
+	}
+}
+
+func TestMapCuisineSlug_Unknown(t *testing.T) {
+	result := savedrecipe.MapCuisineSlug("peruvian")
+	if result != "other" {
+		t.Errorf("MapCuisineSlug(peruvian) = %q, want %q", result, "other")
+	}
+}
+
+func TestMapCuisineSlug_Empty(t *testing.T) {
+	result := savedrecipe.MapCuisineSlug("")
+	if result != "other" {
+		t.Errorf("MapCuisineSlug() = %q, want %q", result, "other")
+	}
+}
+
+func TestMapCuisineSlug_CaseSensitive(t *testing.T) {
+	// The function does NOT lowercase — "ITALIAN" is unknown and falls back to "other".
+	result := savedrecipe.MapCuisineSlug("ITALIAN")
+	if result != "other" {
+		t.Errorf("MapCuisineSlug(ITALIAN) = %q, want %q", result, "other")
+	}
+}