wl_backend: use IN_CLOSE_WRITE instead of IN_MODIFY for inotify

IN_MODIFY fires during the write, before the file is fully written.
The Wayland event loop's 16ms dispatch catches this almost instantly,
reading stale/partial content. IN_CLOSE_WRITE fires after the writer
closes the file, guaranteeing the content is complete.

This fixes the 'one step behind' issue where background changes only
appeared on the second apply.

src/backend/wayland/wl_backend.c

@@ -3281,7 +3281,7 @@ static void wl_handle_inotify_events(void)
             }
             wPreferences.flags.noupdates = 1;
         }
-        if ((pevent->mask & IN_MODIFY) && oneShotFlag == 0) {
+        if ((pevent->mask & IN_CLOSE_WRITE) && oneShotFlag == 0) {
             wDefaultsCheckDomains(NULL);
             oneShotFlag = 1;
         }