Explicit support requests need alert-level idempotency, not issue-existence dedupe

Do not deduplicate an explicit support request solely by whether a support issue already exists. Existing issues may be active, resolved, or silenced. Reactivate the support episode transactionally, update its current blocked step, then claim the outbound alert with a separate durable idempotency key scoped to the workflow and a bounded server-time window. Only a newly claimed event should route and send; replays may return success without duplicating the alert.