Feature: Russian language support & Vehicle Requests improvements

- Add Russian language support (title_ru, subtitle_ru) for hero banners
- Add fuel/transmission translations for Mongolian (경유→Дизель, 오토→Автомат)
- Improve Vehicle Requests admin page:
  - Display real request ID and user email
  - Show detailed request info (maker, grade, year, fuel, mileage)
  - Replace modal search with Cars page integration
- Add "Add to Request" flow in Cars page for vehicle recommendations
- Fix image URL handling in FilmStripSlider and car detail page

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/hero_banners.py

@@ -23,23 +23,24 @@ ALLOWED_EXTENSIONS = {".jpg", ".jpeg", ".png", ".gif", ".webp"}
 
 
 def get_localized_field(obj, field: str, lang: str) -> Optional[str]:
-    """Get localized field value with fallback to Korean then English"""
+    """Get localized field value with fallback to English"""
+    # 1. 선택된 언어의 필드
     localized = getattr(obj, f"{field}_{lang}", None)
     if localized:
         return localized
-    # Fallback to Korean
-    ko_value = getattr(obj, f"{field}_ko", None)
-    if ko_value:
-        return ko_value
-    # Fallback to English
-    return getattr(obj, f"{field}_en", None)
+    # 2. 영어 폴백
+    en_value = getattr(obj, f"{field}_en", None)
+    if en_value:
+        return en_value
+    # 3. 한국어 폴백 (마지막 수단)
+    return getattr(obj, f"{field}_ko", None)
 
 
 # ==================== Public Endpoints ====================
 
 @router.get("/", response_model=List[HeroBannerLocalizedResponse])
 def get_hero_banners(
-    lang: str = Query("ko", regex="^(ko|en|mn)$"),
+    lang: str = Query("ko", regex="^(ko|en|mn|ru)$"),
     db: Session = Depends(get_db)
 ):
     """활성 히어로 배너 목록 조회 (Public)"""