fix: openai endpoint bad request

[blakkd]

Fixes the JSON schema issue

{
  "Invalid request": {
    "error": {
      "code": 400,
      "message": "JSON schema conversion failed:\nUnrecognized schema: {\"description\":\"Optional metadata to store with the plan item.\"}"
    }
  }
}

That made it for me for when serving with llama-cpp. But no pressure, I don't know if this is a good approach this was a quick fix using gpt-oss-20b!

[stippi]

LGTM