xsettings: start after treeland-sd.service to avoid crash on Wayland

The XSettings service uses QGuiApplication with the xcb platform plugin,
which requires an X11 connection (via XWayland). On treeland/Wayland
sessions, XWayland may not be ready yet when this service starts as part
of dde-session-pre.target, causing a crash loop.

Add After=treeland-sd.service to ensure the service only starts after
treeland (which launches XWayland) is ready. This ordering is safely
ignored on pure X11 sessions where treeland-sd.service doesn't exist.

Author: felixonmars

src/plugin-qt/xsettings/misc/org.deepin.dde.XSettings1.service

@@ -6,6 +6,7 @@ CollectMode=inactive-or-failed
 
 PartOf=dde-session-pre.target
 Before=dde-session-pre.target
+After=treeland-sd.service
 
 Before=org.dde.session.Daemon1.service