feat(briefing): register 05:10 KST APScheduler cron

매일 KST 05:10 morning_briefing_run 자동 실행. scheduler timezone=Asia/Seoul
이라 hour=5 minute=10 만 명시. Phase 4 04:00 cron 종료 후 70분 buffer + MLX
semaphore 충돌 회피.

app/main.py

@@ -39,6 +39,7 @@ async def lifespan(app: FastAPI):
     from apscheduler.schedulers.asyncio import AsyncIOScheduler
     from apscheduler.triggers.cron import CronTrigger
     from services.search.query_analyzer import prewarm_analyzer
+    from workers.briefing_worker import run as morning_briefing_run
     from workers.daily_digest import run as daily_digest_run
     from workers.digest_worker import run as global_digest_run
     from workers.file_watcher import watch_inbox
@@ -94,6 +95,7 @@ async def lifespan(app: FastAPI):
     scheduler.add_job(mailplus_run, CronTrigger(hour=18), id="mailplus_evening")
     scheduler.add_job(daily_digest_run, CronTrigger(hour=20), id="daily_digest")
     scheduler.add_job(global_digest_run, CronTrigger(hour=4, minute=0), id="global_digest")
+    scheduler.add_job(morning_briefing_run, CronTrigger(hour=5, minute=10), id="morning_briefing")
     scheduler.add_job(news_collector_run, "interval", hours=6, id="news_collector")
     scheduler.start()