fix: 4차 리뷰 — 중복 keyframes 제거, useEffect deps 수정

- index.css 중복 @keyframes toast-in 제거 (Toast.css에 정의)
- DownloadSection useEffect deps [] → [loadInfo]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/DownloadSection.jsx

@@ -22,7 +22,7 @@ export default function DownloadSection() {
       .catch(() => { setLoadError(true); setReady(true); });
   }, []);
 
-  useEffect(() => { loadInfo(); }, []);
+  useEffect(() => { loadInfo(); }, [loadInfo]);
 
   const handlePlay = async () => {
     if (!user) {