Replace the user-mode kiosk service with a system unit that runs cage
(single-app Wayland compositor) on tty1 as a dedicated unprivileged
user. No desktop, no display manager, auto-restart on crash via
Restart=always.
setup-pi-kiosk.sh provisions the user, installs cage + seatd, disables
any display manager, points default.target at multi-user, drops the
PAM stack, and enables the service. Idempotent.
Screen wake "auto-login": with no DM and no lockscreen, DPMS-driven
sleep just turns the panel back on — the kiosk process is already
running.
