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.

Start by reviewing the roadmap issue's Value Prop and Expected Outcome for the intended public monitoring alert workflow. The payload names no repository files, tests, or entry points, so implementation scope and completion checks would need to be established before work can begin.

索引モデルが issue の本文から書いたものです。