Worker rejection of a pre-claimed session

Allows a worker to reject a pre-claimed session (e.g. host capacity changed, workarea refused, or daemon is draining). Releases the claim and re-queues the session preserving its original priority. The original `QueuedWork` item must be supplied so the platform can re-enqueue without losing fields.

curl -X POST "https://example.com/api/sessions/string/nack" \  -H "Content-Type: application/json" \  -d '{    "workerId": "string",    "work": {      "sessionId": "string",      "issueId": "string",      "issueIdentifier": "string",      "priority": 0,      "queuedAt": 0    }  }'

{
  "nacked": true,
  "sessionId": "string",
  "requeued": true
}

{
  "error": "Session not found"
}

{
  "error": "Session not found"
}

{
  "error": "Session not found"
}