fix: ESLint react-hooks 최신 규칙 호환

- useCallback → 일반 함수 + eslint-disable (초기 데이터 fetch)
- ToastProvider: useCallback 프로퍼티 할당 → useMemo 객체 패턴
- SSAFYCallbackPage: eslint-disable-line 추가

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

src/components/DownloadSection.jsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useAuth } from '../context/useAuth';
 import { getDownloadInfo } from '../api/download';
@@ -14,15 +14,16 @@ export default function DownloadSection() {
   const { user } = useAuth();
   const navigate = useNavigate();
 
-  const loadInfo = useCallback(() => {
+  const loadInfo = () => {
     setReady(false);
     setLoadError(false);
     getDownloadInfo()
       .then((data) => { setInfo(data); setReady(true); })
       .catch(() => { setLoadError(true); setReady(true); });
-  }, []);
+  };
 
-  useEffect(() => { loadInfo(); }, [loadInfo]);
+  // eslint-disable-next-line react-hooks/set-state-in-effect -- initial data fetch on mount
+  useEffect(() => { loadInfo(); }, []);
 
   const handlePlay = async () => {
     if (!user) {