refactor: Remove unused DB translation system

Static dictionary (i18n.ts CAR_TRANSLATIONS) already covers all terms.
DB translations table had only 179 entries used as fallback and was
never actually reached. Simplifies useTranslate hook to static-only.
DB table preserved for safety.

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

backend/app/models/__init__.py

@@ -2,7 +2,6 @@ from .car import CarMaker, CarModel, Car, CarImage, CarOption
 from .user import User, CarView, PerformanceCheckView, ChargeHistory, VerificationCode
 from .inquiry import Inquiry, InquiryMessage, InquiryStatus, InquiryCategory
 from .hero_banner import HeroBanner, HeroBannerSettings
-from .translation import Translation
 from .cache import CarCache, CarDetailCache, CacheRequestQueue
 from .settings import SystemSettings
 from .vehicle_request import VehicleRequest, RequestVehicle, PurchasedVehicle
@@ -40,7 +39,6 @@ __all__ = [
     "InquiryCategory",
     "HeroBanner",
     "HeroBannerSettings",
-    "Translation",
     "CarCache",
     "CarDetailCache",
     "CacheRequestQueue",