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>

presence.service

@@ -0,0 +1,19 @@
+# systemd --user unit. Enable it as the kiosk user once ~/.config/presence/config
+# exists (see /usr/share/doc/presence/config.example):
+#   systemctl --user enable --now presence
+# Commands run with the user's environment as the manager sees it; swaymsg
+# finds the sway socket by itself, other tools may need
+#   exec systemctl --user import-environment WAYLAND_DISPLAY SWAYSOCK
+# in the sway config.
+[Unit]
+Description=BLE proximity events for the screen
+Documentation=file:///usr/share/doc/presence/README.md
+ConditionPathExists=%E/presence/config
+
+[Service]
+ExecStart=/usr/bin/presence --config %E/presence/config
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=default.target