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/db.py

@@ -86,6 +86,17 @@ def init_db() -> None:
             CREATE INDEX IF NOT EXISTS idx_conv_chat
             ON conversation_messages(chat_id, created_at DESC)
         """)
+        conn.execute("""
+            CREATE TABLE IF NOT EXISTS youtube_research_jobs (
+                id               INTEGER PRIMARY KEY AUTOINCREMENT,
+                status           TEXT NOT NULL DEFAULT 'running',
+                countries        TEXT NOT NULL DEFAULT '[]',
+                trends_collected INTEGER NOT NULL DEFAULT 0,
+                error            TEXT,
+                started_at       TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now')),
+                completed_at     TEXT
+            )
+        """)
         # Seed default agent configs
         for agent_id, name in [
             ("stock", "주식 트레이더"),
@@ -93,6 +104,7 @@ def init_db() -> None:
             ("blog", "블로그 마케터"),
             ("realestate", "청약 애널리스트"),
             ("lotto", "로또 큐레이터"),
+            ("youtube", "YouTube 리서치"),
         ]:
             conn.execute(
                 "INSERT OR IGNORE INTO agent_config(agent_id, display_name) VALUES(?,?)",
@@ -501,3 +513,45 @@ def get_activity_feed(limit: int = 50, offset: int = 0) -> dict:
         items.append(item)
 
     return {"items": items, "total": total}
+
+
+# ── youtube_research_jobs CRUD ────────────────────────────────────────────────
+
+def add_youtube_research_job(countries: list) -> int:
+    with _conn() as conn:
+        conn.execute(
+            "INSERT INTO youtube_research_jobs (countries) VALUES (?)",
+            (json.dumps(countries),),
+        )
+        return conn.execute("SELECT last_insert_rowid()").fetchone()[0]
+
+
+def update_youtube_research_job(
+    job_id: int, status: str, trends_collected: int, error: Optional[str] = None
+) -> None:
+    with _conn() as conn:
+        conn.execute(
+            """UPDATE youtube_research_jobs
+               SET status=?, trends_collected=?, error=?,
+                   completed_at=strftime('%Y-%m-%dT%H:%M:%fZ','now')
+               WHERE id=?""",
+            (status, trends_collected, error, job_id),
+        )
+
+
+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"
+        ).fetchone()
+    if not row:
+        return None
+    return {
+        "id":               row["id"],
+        "status":           row["status"],
+        "countries":        json.loads(row["countries"]),
+        "trends_collected": row["trends_collected"],
+        "error":            row["error"],
+        "started_at":       row["started_at"],
+        "completed_at":     row["completed_at"],
+    }