curl --request PATCH \
  --url http://localhost:8080/api/agents/{agentId}/unassign \
  --header 'X-API-KEY: <api-key>' \
  --header 'X-API-SECRET: <api-key>'

{
  "message": "Post-call webhook unassigned successfully",
  "status": "success",
  "error": null,
  "data": {
    "agent_id": "agent_123",
    "post_call_webhook_id": null
  }
}