fix(agent-office): YouTubeResearchAgent 품질 개선 (동시실행 가드·에러 로깅·타입 수정)

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

agent-office/app/db.py

@@ -542,7 +542,7 @@ def update_youtube_research_job(
 def get_latest_youtube_research_job() -> Optional[Dict[str, Any]]:
     with _conn() as conn:
         row = conn.execute(
-            "SELECT * FROM youtube_research_jobs ORDER BY started_at DESC LIMIT 1"
+            "SELECT * FROM youtube_research_jobs ORDER BY id DESC LIMIT 1"
         ).fetchone()
     if not row:
         return None