Public monitoring ability to dismiss/reopen alerts [Public Preview]

### Value Prop
You can now dismiss and reopen public monitoring alerts, with an optional comment explaining your decision. This makes it easier to triage large volumes of alerts and keep your security workflow organized. Teams can quickly mark resolved or irrelevant alerts as closed, so the active alert list stays focused on what actually needs attention.

### Expected Outcome
Security teams working with high volumes of public monitoring alerts gain a faster, more structured way to manage their alert queues. By enabling dismissal and reopening with optional context, teams can reduce noise and make triage more consistent across contributors. The result is a cleaner, more actionable view of real security signals.

首先查看 roadmap issue 的 Value Prop 和 Expected Outcome，了解预期的公共监控告警工作流。payload 未列出任何 repository 文件、测试或入口点，因此需要先确定实现范围和完成检查项，然后才能开始工作。

由索引模型根据 Issue 内容生成。