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>

frontend/src/components/FilmStripSlider.tsx

@@ -338,15 +338,23 @@ const getImageUrl = (url: string): string => {
 
 // Helper to get localized title/subtitle based on language
 function getLocalizedText(banner: HeroBanner, field: 'title' | 'subtitle', language: Language): string {
-  // Public API returns localized single field (title, subtitle)
-  const directField = banner[field as keyof HeroBanner] as string | undefined;
-  if (directField) {
-    return directField;
-  }
-  // Admin API returns multi-language fields (title_ko, title_en, etc.)
+  // 1. 먼저 선택된 언어의 필드 확인 (title_mn, title_en, etc.)
   const langKey = `${field}_${language}` as keyof HeroBanner;
+  const langValue = banner[langKey] as string | undefined;
+  if (langValue) {
+    return langValue;
+  }
+
+  // 2. 영어 폴백
   const enKey = `${field}_en` as keyof HeroBanner;
-  return (banner[langKey] as string) || (banner[enKey] as string) || '';
+  const enValue = banner[enKey] as string | undefined;
+  if (enValue) {
+    return enValue;
+  }
+
+  // 3. 마지막으로 직접 필드 (API가 단일 필드로 반환하는 경우)
+  const directField = banner[field as keyof HeroBanner] as string | undefined;
+  return directField || '';
 }
 
 function BannerCard({ banner, width, height }: BannerCardProps) {