fix(webui): drop App markdown warmup; keep preloadMarkdownText export

Startup no longer triggers preloadMarkdownText (#3746). Restore the named
export so MessageBubble can still warm the lazy markdown chunk when the
reasoning panel opens (compatible with current main).

Co-authored-by: Cursor <cursoragent@cursor.com>

webui/src/App.tsx

@@ -157,8 +157,6 @@ export default function App() {
     return bootstrapWithSecret(saved);
   }, [bootstrapWithSecret]);
 
-
-
   if (state.status === "loading") {
     return (
       <div className="flex h-full w-full items-center justify-center">