feat: improve memory cleanup when plan approve

Author: dori

src/mcp_as_a_judge/db/providers/sqlite_provider.py

@@ -7,6 +7,7 @@
 
 import time
 import uuid
+from typing import cast
 
 from sqlalchemy import create_engine, delete, func
 from sqlmodel import Session, SQLModel, asc, desc, select
@@ -349,7 +350,7 @@ async def delete_previous_plan(self, session_id: str) -> None:
                     ConversationRecord.id.in_(record_ids_to_delete)
                 )
                 # Use the underlying SQLAlchemy session for delete operations
-                session.exec(delete_stmt)
+                session.execute(delete_stmt)
                 session.commit()
 
                 logger.info(