feat: Add admin settings for dealer comment & domestic cost, enhance visitor country stats

- Add show_dealer_comment toggle to admin settings
- Add domestic_export_customs_krw setting for cost page
- Cost page now uses dynamic settings instead of hardcoded values
- Enhance Visitor Stats with dedicated Country Stats card with flags
- Fix hero_banners API route ordering (422 error fix)
- Fix banner toggle logic to check HeroBanner table instead of car.is_banner
- Add country flag emojis for 23+ countries

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

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

backend/app/schemas/settings.py

@@ -15,6 +15,11 @@ class SystemSettingsUpdate(BaseModel):
     cache_ttl_hours: Optional[int] = None
     container_logistics_usd: Optional[int] = None
     shoring_cost_usd: Optional[int] = None
+    domestic_export_customs_krw: Optional[int] = None
+    show_dealer_comment: Optional[bool] = None
+    referral_reward_enabled: Optional[bool] = None
+    referral_reward_percent: Optional[float] = None
+    referral_reward_type: Optional[str] = None
 
 
 class SystemSettingsResponse(BaseModel):
@@ -30,6 +35,11 @@ class SystemSettingsResponse(BaseModel):
     cache_ttl_hours: int
     container_logistics_usd: int
     shoring_cost_usd: int
+    domestic_export_customs_krw: int = 1150000
+    show_dealer_comment: bool = True
+    referral_reward_enabled: bool = True
+    referral_reward_percent: float = 10.0
+    referral_reward_type: str = "one_time"
     created_at: Optional[datetime] = None
     updated_at: Optional[datetime] = None