Long error messages when connecting to a Coder deployment could causethe window to overflow. Simmilar issue as:#146.Errors are now limited to 500px by the ScrollViewer component.<img width="325" height="913" alt="image"src="https://github.com/user-attachments/assets/571503c5-9c6f-4d33-b9f8-1ae3530f72fa"/>---------Co-authored-by: Dean Sheather <dean@deansheather.com>

Reworks the TestHttpServer threading to:- Use an async method instead (so we can wait with a cancellation token)- Use a cancellation token while awaiting the listener to return arequest- `GetContext()` doesn't take a CTS directly, so we call`Task.WaitAsync(CancellationToken ct)` instead- Adds some exception handling and discarding where necessary to ignoreexpected errors during shutdownClosescoder/internal#603