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/models/settings.py

@@ -29,6 +29,12 @@ class SystemSettings(Base):
     container_logistics_usd = Column(Integer, default=3600)  # 컨테이너 물류비 $3,600
     shoring_cost_usd = Column(Integer, default=300)  # 쇼링비 (컨테이너 고정) $300
 
+    # 국내비용 + 수출통관비용 (KRW)
+    domestic_export_customs_krw = Column(Integer, default=1150000)  # ₩1,150,000
+
+    # 딜러 코멘트 표시 설정
+    show_dealer_comment = Column(Boolean, default=True)  # 딜러 코멘트 표시 여부
+
     # 레퍼럴 보상 설정
     referral_reward_enabled = Column(Boolean, default=True)  # 레퍼럴 보상 활성화
     referral_reward_percent = Column(Float, default=10.0)  # 보상 비율 (기본 10%)