feat: add webhook node limit validation (max 5 per workflow)

- Add MAX_WEBHOOK_NODES_PER_WORKFLOW constant set to 5
- Validate webhook node count in sync_webhook_relationships method
- Raise ValueError when workflow exceeds webhook node limit
- Block workflow save when limit is exceeded to ensure data integrity
- Provide clear error message indicating current count and maximum allowed

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

api/controllers/console/app/workflow_trigger.py

@@ -167,7 +167,7 @@ class AppTriggersApi(Resource):
         """Get app triggers list"""
         assert isinstance(current_user, Account)
         assert current_user.current_tenant_id is not None
-        
+
         with Session(db.engine) as session:
             # Get all triggers for this app using select API
             triggers = (