White screen appears if search backend proxy is misconfigured

[sashakames]

We had an incident at ORNL where the /proxy routes for the backend disappeared. This caused the frontend callout to the search endpoint to "feedback on itself" because the route was going back to the fronted but with a 404 handled by React. API calls should be tested to ensure they are receiving a properly structured response. Better yet, we should have a test to ensure that the error handler works.