Register a webhook so long-running jobs (render/compose/media) notify you instead of blocking on wait_job. Body: `url` (https, must pass SSRF checks) + `events` (see the WebhookEvent enum). DELIVERY: each event is a POST with body `{ event, timestamp, projectId?, data }` and Standard-Webhooks headers `webhook-id`, `webhook-timestamp`, `webhook-signature: v1,<base64>` (+ `x-cueframe-event`). The `secret` (`whsec_<base64>`) is returned ONCE here — verify the raw body with `new…