Stop a running desktop display manager during a live install

On a Pi OS Desktop image lightdm keeps display :0 until the next reboot,
so the kiosk X server failed with 'server already running'. Disabled
display managers are recorded and re-enabled by uninstall.sh.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

install.sh

@@ -243,11 +243,18 @@ for cmdline in /boot/firmware/cmdline.txt /boot/cmdline.txt; do
   fi
 done
 
-# A desktop display manager would fight over vt7.
+# A desktop display manager would fight over vt7 and display :0 (Pi OS Desktop images).
+# uninstall.sh re-enables the ones recorded here.
 for dm in lightdm.service gdm3.service sddm.service; do
   if systemctl is-enabled --quiet "$dm" 2>/dev/null; then
     warn "$dm wordt uitgeschakeld (de kiosk gebruikt een eigen minimale X-sessie)."
     systemctl disable "$dm" 2>/dev/null || true
+    grep -qx "$dm" /var/lib/voxip-kiosk/disabled-display-managers 2>/dev/null \
+      || echo "$dm" >> /var/lib/voxip-kiosk/disabled-display-managers
+  fi
+  if [[ $LIVE -eq 1 ]] && systemctl is-active --quiet "$dm" 2>/dev/null; then
+    warn "$dm wordt gestopt: de desktop op het scherm sluit nu af."
+    systemctl stop "$dm" || true
   fi
 done