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/models/hero_banner.py

@@ -38,11 +38,13 @@ class HeroBanner(Base):
     title_ko = Column(String(100))
     title_en = Column(String(100))
     title_mn = Column(String(100))  # 몽골어
+    title_ru = Column(String(100))  # 러시아어
 
     # 다국어 서브타이틀
     subtitle_ko = Column(String(200))
     subtitle_en = Column(String(200))
     subtitle_mn = Column(String(200))
+    subtitle_ru = Column(String(200))  # 러시아어
 
     # 이미지 URL
     image_url = Column(String(500), nullable=False)