Nicer looking errors for response errors in panel chat

Discussion in https://github.com/microsoft/vscode-copilot-issues/issues/336

These don't look nice, could still be improved

<img width="972" height="388" alt="Image" src="https://github.com/user-attachments/assets/a9ff4c67-2160-4bb9-a6cd-8b06d88c24fa" />