Improve default unauthorized error

It looks like this currently

<img width="638" height="366" alt="Image" src="https://github.com/user-attachments/assets/5a0f38ac-483b-4a0a-9216-d2f94dbb9ac0" />

It should give us some information about what this is, why you see it and ideally even point the user to a configurable URL. Maybe this is an opportunity to streamline the configuration aligned with bfabric-web-apps.