Error: feature named `pageObserver` was not found

## Error

```
feature named `pageObserver` was not found
```

## Tracking Details
- **Project**: exercism-js
- **Sentry**: [Error: feature named `pageObserver` was not found](https://thalamus-ai.sentry.io/issues/100230745/)
- **Culprit**: https://exercism.org/users/sign_in
- **First seen:** Mar 2, 2026