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/index.css

@@ -30,15 +30,4 @@ a {
 
 a:hover {
   opacity: 0.85;
-}
-
-@keyframes toast-in {
-  from {
-    opacity: 0;
-    transform: translateX(40px);
-  }
-  to {
-    opacity: 1;
-    transform: translateX(0);
-  }
-}
+}