feat: Add bulletin board system

- Add BoardCategory and BoardPost models with multi-language support
- Add bulletin API endpoints (CRUD, notice toggle, pin toggle)
- Add board_enabled setting to control menu visibility
- Create frontend board pages (list, detail, write, edit)
- Create admin board management and category management pages
- Update Header.tsx with conditional Board menu between Inquiry and Contact Us
- Update admin settings with board_enabled toggle
- Add Board menu to admin sidebar

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

backend/app/main.py

@@ -9,7 +9,7 @@ import asyncio
 from apscheduler.schedulers.asyncio import AsyncIOScheduler
 from apscheduler.triggers.cron import CronTrigger
 from .database import engine, Base, SessionLocal
-from .api import cars, auth, inquiries, hero_banners, carmodoo, translations, cc, settings, vehicle_requests, dealer, vehicle_share, withdrawal, referral, notification, dashboard, push, exchange_rate, verification, visitor, sns_share
+from .api import cars, auth, inquiries, hero_banners, carmodoo, translations, cc, settings, vehicle_requests, dealer, vehicle_share, withdrawal, referral, notification, dashboard, push, exchange_rate, verification, visitor, sns_share, bulletin
 from .config import get_settings
 from .services.exchange_rate_service import update_exchange_rates
 from .services.visitor_service import aggregate_daily_stats, cleanup_old_visitor_logs
@@ -238,6 +238,7 @@ app.include_router(exchange_rate.router)
 app.include_router(verification.router, prefix="/api")
 app.include_router(visitor.router, prefix="/api")
 app.include_router(sns_share.router, prefix="/api")
+app.include_router(bulletin.router, prefix="/api")
 
 
 @app.get("/")