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/schemas/settings.py

@@ -12,6 +12,7 @@ class SystemSettingsUpdate(BaseModel):
     cc_per_view: Optional[int] = None
     cc_signup_bonus: Optional[int] = None
     cars_per_cc: Optional[int] = None
+    cc_per_banner_view: Optional[float] = None
     cache_ttl_hours: Optional[int] = None
     container_logistics_usd: Optional[int] = None
     shoring_cost_usd: Optional[int] = None
@@ -32,6 +33,7 @@ class SystemSettingsResponse(BaseModel):
     cc_per_view: int
     cc_signup_bonus: int
     cars_per_cc: int
+    cc_per_banner_view: float = 0.1
     cache_ttl_hours: int
     container_logistics_usd: int
     shoring_cost_usd: int