#78 FTX-78: DLQ admin APIs (P2)

GET /v1/webhooks/deliveries?state= , GET .../{id}, POST .../{id}/requeue (atomic UPDATE WHERE state=dead RETURNING, 409 otherwise), bulk requeue capped 1000; mail equivalents /v1/notifications/outbox; perms webhook:manage/tenant:admin, platform cross-tenant. Phase 7.