Get a webhook delivery

Returns the envelope CONTENT this delivery carried, as the projection for ITS endpoint — the same projection that composes real deliveries, so a content block the endpoint did not opt into is absent here exactly as it was absent on the wire. It is not an archive of the transmitted bytes: we store none, so this is rebuilt from the stored event and is a re-serialization — never verify a signature against it. `payloadConfig` is returned alongside because it is read as it is NOW; if the endpoint’s opt-ins changed after this delivery, you are seeing what it would receive today. Payloads disappear with their event after the retention window (410 once the event is pruned). Requires `webhook-payloads.read`, which is separate from `webhooks.manage` and is granted by NO wildcard — including `*` and `webhooks.*` — because for endpoints subscribed to the `outcome` or `transcript` blocks this content includes personal data, including sensitive data. Required scope: `webhook-payloads.read`.