refactor: fsd 구조로 변환

src/widgets/lobby-background/ui/LobbyBackgroundWidget.tsx

@@ -0,0 +1,9 @@
+import { ConstellationScene } from '@/features/lobby-starfield';
+
+export function LobbyBackgroundWidget() {
+  return (
+    <div className="fixed inset-0 z-0 overflow-hidden pointer-events-none bg-[radial-gradient(ellipse_at_center,_var(--tw-gradient-stops))] from-slate-900 via-slate-950 to-black">
+      <ConstellationScene />
+    </div>
+  );
+}