feat(moonarch-git): package battery conservation mode assets

Add udev rule and systemd service to PKGBUILD. Create /var/lib/moonarch
state directory and enable batsaver restore service on laptops in the
post-install hook.

moonarch-git/moonarch.install

@@ -71,6 +71,12 @@ post_install() {
     rm -f /usr/local/bin/swww /usr/local/bin/swww-daemon 2>/dev/null || true
     rm -f /usr/local/bin/moonarch-update 2>/dev/null || true
 
+    # Battery conservation mode: create state directory and enable restore service
+    install -dm775 -g wheel /var/lib/moonarch
+    if [ -f /sys/class/power_supply/BAT0/charge_control_end_threshold ]; then
+        systemctl enable moonarch-batsaver.service 2>/dev/null || true
+    fi
+
     echo "==> Moonarch defaults installed."
     echo "==> For first-time setup run: /opt/moonarch/scripts/post-install.sh"
     echo "==> This enables services and configures firewall."