Config file, user service, and a build container that can see bluez

`--config` reads the same directives as the command line, one per line with
the rest of the line as the command, so a unit can carry the kiosk's events
without shell quoting. presence.service is a systemd --user unit that runs it
from ~/.config/presence/config, restarts on failure, and only starts when the
file exists; config.example is the starting point.

The x86_64 release job failed on makepkg's runtime dependency check because
bluez was not in the container. It is now.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

config.example

@@ -0,0 +1,14 @@
+# ~/.config/presence/config: one directive per line. The rest of the line
+# after the keyword (and the seconds, for absent) is the command, verbatim.
+# Pick rssi from `presence --calibrate` at the installed screen; -58 is a
+# starting point, not a measurement.
+
+rssi -58
+# window 5
+# hits 3
+# stale 15
+# adapter hci0
+# ignore AA:BB:CC:DD:EE:FF
+
+present swaymsg "output * power on"
+absent 600 swaymsg "output * power off"