Add missing last_alert_message column migration for key_monitors.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/key_monitor/key_monitor_schema_lib.py

@@ -7,6 +7,7 @@ from typing import Any
 def ensure_key_monitor_schema(conn: Any) -> None:
     for sql in (
         "ALTER TABLE key_monitors ADD COLUMN last_mark_price REAL",
+        "ALTER TABLE key_monitors ADD COLUMN last_alert_message TEXT",
     ):
         try:
             conn.execute(sql)