When force_auth is on, the guest homepage still loads, but /api/v1/server
returns {"error":"ApiErrorUnauthorized"}. BackendErrorState treated that
the same as a down backend.
Match that error exactly and show a login title, description, and a
button to /dashboard. Other errors keep the old copy and the raw message.
zh-TW is unchanged: that file uses spaces, and biome would reformat the
whole translation.
