feat: add BoardWebhook updates on agent deletion

backend/app/services/openclaw/admin_service.py

@@ -16,6 +16,7 @@ from app.db import crud
 from app.models.activity_events import ActivityEvent
 from app.models.agents import Agent
 from app.models.approvals import Approval
+from app.models.board_webhooks import BoardWebhook
 from app.models.gateways import Gateway
 from app.models.tasks import Task
 from app.schemas.gateways import GatewayTemplatesSyncResult
@@ -340,6 +341,14 @@ class GatewayAdminLifecycleService(OpenClawDBService):
             agent_id=None,
             commit=False,
         )
+        await crud.update_where(
+            self.session,
+            BoardWebhook,
+            col(BoardWebhook.agent_id) == agent_id,
+            agent_id=None,
+            updated_at=now,
+            commit=False,
+        )
 
     async def sync_templates(
         self,