Webhook DLQ

Deliveries that exhausted the retry budget (5×). Manual intervention only — auto-retry past the initial attempts is intentionally absent to avoid storm-on-recovery patterns.

Requeue fires POST /v1/admin/webhook-dlq/:id/requeue — delivery resets to attempt=1 + retry budget refreshes. Audit row records admin id + delivery id + reason. Discard hard-deletes the entry; payload is unrecoverable.