UI Tests

- Focus on unit tests and simple smoke tests, use snapshot tests for those components that don't change often & where the output is deterministic
- Backend responses can be mocked
- See the [testing section](https://create-react-app.dev/docs/running-tests/) of create-react-app on how to setup and run tests with create-react-app

Start with the create-react-app testing section linked in the issue to understand how tests are set up and run. Review the UI components and backend calls to identify unit and smoke-test targets, using mocked responses where needed. Done means the appropriate UI tests exist, with snapshots only for deterministic, stable components.

Written by the indexing model from the issue text.