fix(desktop): scope dark styles and restore dialog blur

apps/desktop/src/lib/app/dialogBackdrop.ts

@@ -0,0 +1,24 @@
+const DIALOG_BACKDROP_CLASS = "dbx-dialog-backdrop-active";
+
+let dialogBackdropObserver: MutationObserver | undefined;
+
+function hasDialogOverlay(): boolean {
+  return Array.from(document.body.children).some((child) => child.matches('[data-slot="dialog-overlay"]') || child.querySelector('[data-slot="dialog-overlay"]'));
+}
+
+function syncDialogBackdrop() {
+  document.documentElement.classList.toggle(DIALOG_BACKDROP_CLASS, hasDialogOverlay());
+}
+
+export function startDialogBackdropSync() {
+  if (typeof document === "undefined" || dialogBackdropObserver) return;
+  dialogBackdropObserver = new MutationObserver(syncDialogBackdrop);
+  dialogBackdropObserver.observe(document.body, { childList: true });
+  syncDialogBackdrop();
+}
+
+export function stopDialogBackdropSync() {
+  dialogBackdropObserver?.disconnect();
+  dialogBackdropObserver = undefined;
+  document.documentElement.classList.remove(DIALOG_BACKDROP_CLASS);
+}