Fetch tool should better indicate in UI when the request fails

1. Ask the fetch tool to make a request that fails with a 404, such as `fetch the contents of http://microsoft.com/no-such-link`


**Bug**
Looking at the UI, it's not very clear that this request failed

<img width="505" height="300" alt="Image" src="https://github.com/user-attachments/assets/5ac5ab57-ceae-43d6-92c4-dbffce5f183c" />

I'd expect some kind of warning/error icon