Forwarding…
The Arnold UI is served by the device itself. This page only forwards
to a device: pass ?device=<ip-or-hostname> to jump to a
specific one, otherwise it forwards to arnold.local (any
device on the LAN answers that name and lists all its peers).
If nothing happens, click the link above — on first use your
browser will show a certificate warning for the device's self-signed
certificate; accept it to continue.