Add configurable CC cost for banner vehicle PDF/description view

- Add cc_per_banner_view setting to system_settings (default 0.1 CC)
- Update car detail page to use dynamic CC value from settings
- Add CC per Banner View field in admin settings page
- Replace hardcoded 0.1 CC with configurable value

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

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

backend/app/api/settings.py

@@ -26,6 +26,7 @@ def get_or_create_settings(db: Session) -> SystemSettings:
             cc_per_usdc=1,  # 1 USD = 1 CC
             cc_per_view=1,  # 차량 상세 조회 시 1 CC
             cars_per_cc=3,  # 1 CC = 3 recommended vehicles per request
+            cc_per_banner_view=0.1,  # 배너 차량 PDF/상세 보기 비용
             cc_signup_bonus=3,  # 3 CC free on signup
             cache_ttl_hours=2,
             container_logistics_usd=3600,