Improve loading speed of desktop app (#4865)

# Description of Changes
Improve loading speed of desktop app by loading a default config until
the backend has spawned.

frontend/src/desktop/components/DesktopConfigSync.tsx

@@ -0,0 +1,23 @@
+import { useEffect, useRef } from 'react';
+import { useBackendHealth } from '@app/hooks/useBackendHealth';
+import { useAppConfig } from '@app/contexts/AppConfigContext';
+
+/**
+ * Desktop-only bridge that refetches the app config once the bundled backend
+ * becomes healthy (and whenever it restarts). Keeps the UI responsive by using
+ * default config until the real config is available.
+ */
+export function DesktopConfigSync() {
+  const { status } = useBackendHealth();
+  const { refetch } = useAppConfig();
+  const previousStatus = useRef(status);
+
+  useEffect(() => {
+    if (status === 'healthy' && previousStatus.current !== 'healthy') {
+      refetch();
+    }
+    previousStatus.current = status;
+  }, [status, refetch]);
+
+  return null;
+}