Replace the Haar-cascade face detector with lightweight frame-differencing
motion detection so the daemon can poll every 20s (backing off to 120s under
heavy CPU/RAM load) without adding noticeable overhead.
Presence detection now shares caffeine's systemd-inhibit lock instead of
holding its own, so the caffeine status widget reflects either source. A new
ownership flag ensures the daemon only ever releases a lock it acquired
itself, so a manually-started caffeine session is never interrupted by the
user stepping away. Also re-enables the daemon in hyprlua's autostart (was
previously only wired up for niri).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>