xhigh reasoning effort is missing short description

Notice how the xhigh reasoning effort does not have a description. We should fix this. Ideally this description already comes from CAPI and we just surface it?

<img width="785" height="154" alt="Image" src="https://github.com/user-attachments/assets/6f60f68d-47b7-41cb-a70f-1972cb5ea73d" />

cc @bhavyaus 