A web view for the power-protection layer, with an offline-safe fallback

The power-protection layer now has a web interface. Until today the only way to see a UPS was a command line on the host it was attached to.

It is deployed in two tiers on purpose. The convenient view aggregates all three units behind single sign-on. Underneath it, each machine also serves its own page directly, depending on nothing else at all - no gateway, no sign-on, no cluster - because the comfortable path runs through the very infrastructure a power failure takes away, which is exactly when someone needs to look.

Neither view can switch anything off. They hold no credentials, and the protocol they speak requires credentials for any command that changes state, so read-only is a property of how they are built rather than a setting that could be changed by mistake.

Tracking post for the changelog entry covering this work.