fix: add missing async_session_factory import in main_scheduler

backend/app/main_scheduler.py

@@ -16,7 +16,7 @@ from apscheduler.triggers.interval import IntervalTrigger
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 
 from app.config import settings
-from app.database import Base
+from app.database import Base, async_session_factory
 
 
 # ── Scheduler-specific engine: longer statement_timeout (30s) ──