feat(agent-office): YouTubeResearchAgent + 스케줄러 + /youtube/research API

- db.py: youtube_research_jobs 테이블 추가 + CRUD 3종 (add/update/get_latest)
- agents/youtube.py: YouTubeResearchAgent 신규 구현 (on_schedule/on_command/on_approval/_run_research/send_weekly_report)
- agents/__init__.py: YouTubeResearchAgent 등록
- scheduler.py: youtube_research(매일 09:00) + youtube_weekly_report(월 08:00) cron 추가
- main.py: POST /api/agent-office/youtube/research + GET /api/agent-office/youtube/research/status 엔드포인트 추가

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent-office/app/scheduler.py

@@ -24,9 +24,21 @@ async def _run_lotto_schedule():
     if agent:
         await agent.on_schedule()
 
+async def _run_youtube_research():
+    agent = AGENT_REGISTRY.get("youtube")
+    if agent:
+        await agent.on_schedule()
+
+async def _send_youtube_weekly_report():
+    agent = AGENT_REGISTRY.get("youtube")
+    if agent:
+        await agent.send_weekly_report()
+
 def init_scheduler():
     scheduler.add_job(_run_stock_schedule, "cron", hour=7, minute=30, id="stock_news")
     scheduler.add_job(_run_blog_schedule, "cron", hour=10, minute=0, id="blog_pipeline")
     scheduler.add_job(_run_lotto_schedule, "cron", day_of_week="mon", hour=7, minute=0, id="lotto_curate")
+    scheduler.add_job(_run_youtube_research, "cron", hour=9, minute=0, id="youtube_research")
+    scheduler.add_job(_send_youtube_weekly_report, "cron", day_of_week="mon", hour=8, minute=0, id="youtube_weekly_report")
     scheduler.add_job(_check_idle_breaks, "interval", seconds=60, id="idle_check")
     scheduler.start()