Startup error in version 8.1.0

### Question and Steps to reproduce

全新安装启动alert_rule表出现缺少字段 总共三个字段prod ，disabled还有update_at，请修复一下创建的sql脚本

### Relevant logs and configurations

```text
2025-07-24 10:25:21.310245 ERROR ormx/ormx.go:68 /home/runner/work/nightingale/nightingale/models/alert_rule.go:1131 Error 1054: Unknown column 'prod' in 'where clause'
[0.072ms] [rows:0] SELECT * FROM `alert_rule` WHERE prod in ('host') AND disabled = 0
2025/07/24 10:25:21 host_alert_rule_targets.go:72: failed to sync targets: Error 1054: Unknown column 'prod' in 'where clause'
```

### Version

8.1.0版本 系统版本RHEL 8 X86

Start with models/alert_rule.go:1131 and the failing query shown in the report, then trace the fresh-install SQL creation script for alert_rule. Verify the schema includes prod, disabled, and update_at, and run a clean installation on MySQL to confirm the startup query and target synchronization no longer fail.

Written by the indexing model from the issue text.