Trash alert

This endpoint trashes a subscription- or customer-scoped alert. The alert is soft-deleted: it stops firing immediately and no longer appears in fetch or list responses, while the underlying record is retained internally for audit.

Plan-level alerts cannot be trashed via the API — disable them instead (POST /v1/alerts/{alert_configuration_id}/disable). Their removal would need to be unwound from every subscription the alert was propagated to, which isn't supported yet.