feat: Toast 알림 시스템 + 어드민 UX 개선

- Toast 알림 컴포넌트 추가 (success/error/warn/info)
- AnnouncementAdmin 초기 로딩 상태 + 에러 표시
- DownloadAdmin 로딩 상태 추가
- UserAdmin/AnnouncementAdmin에 Toast 피드백 적용
- API client 5xx/네트워크 에러 자동 재시도

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

src/App.jsx

@@ -1,6 +1,7 @@
 import { BrowserRouter, Routes, Route, Navigate, useNavigate, useLocation } from 'react-router-dom';
 import { useEffect, useRef } from 'react';
 import { AuthProvider } from './context/AuthContext';
+import { ToastProvider } from './components/toast/ToastProvider';
 import { useAuth } from './context/useAuth';
 import LoginPage from './pages/LoginPage';
 import RegisterPage from './pages/RegisterPage';
@@ -62,7 +63,9 @@ export default function App() {
   return (
     <BrowserRouter>
       <AuthProvider>
+        <ToastProvider>
           <AppRoutes />
+        </ToastProvider>
       </AuthProvider>
     </BrowserRouter>
   );

src/api/client.js

@@ -52,9 +52,20 @@ async function parseResponse(res) {
   return res.json();
 }
 
-export async function apiFetch(path, options = {}) {
+export async function apiFetch(path, options = {}, _retryCount = 0) {
   const token = localStorage.getItem('token');
-  const res = await doFetch(path, options, token);
+  let res;
+
+  try {
+    res = await doFetch(path, options, token);
+  } catch (e) {
+    // 네트워크 에러 (오프라인 등) — 재시도
+    if (_retryCount < 2) {
+      await delay(1000 * (_retryCount + 1));
+      return apiFetch(path, options, _retryCount + 1);
+    }
+    throw e;
+  }
 
   if (res.status === 401) {
     try {
@@ -79,6 +90,16 @@ export async function apiFetch(path, options = {}) {
     }
   }
 
+  // 5xx 서버 에러 — 최대 2회 재시도 (exponential backoff)
+  if (res.status >= 500 && _retryCount < 2) {
+    await delay(1000 * (_retryCount + 1));
+    return apiFetch(path, options, _retryCount + 1);
+  }
+
   if (!res.ok) throw await parseError(res);
   return parseResponse(res);
 }
+
+function delay(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}

src/components/admin/AnnouncementAdmin.jsx

@@ -1,18 +1,27 @@
 import { useState, useEffect, useCallback } from 'react';
 import { getAnnouncements, createAnnouncement, updateAnnouncement, deleteAnnouncement } from '../../api/announcements';
+import { useToast } from '../toast/useToast';
 import './AdminCommon.css';
 
 export default function AnnouncementAdmin() {
+  const toast = useToast();
   const [list, setList] = useState([]);
   const [form, setForm] = useState({ title: '', content: '' });
   const [editingId, setEditingId] = useState(null);
   const [loading, setLoading] = useState(false);
+  const [fetchLoading, setFetchLoading] = useState(true);
   const [error, setError] = useState('');
+  const [fetchError, setFetchError] = useState('');
 
   const load = useCallback(() => {
-    getAnnouncements().then(setList).catch((err) => {
+    setFetchError('');
+    getAnnouncements()
+      .then(setList)
+      .catch((err) => {
         console.error('공지사항 로드 실패:', err);
-    });
+        setFetchError('공지사항을 불러오지 못했습니다.');
+      })
+      .finally(() => setFetchLoading(false));
   }, []);
   useEffect(() => { load(); }, [load]);
 
@@ -30,11 +39,12 @@ export default function AnnouncementAdmin() {
       } else {
         await createAnnouncement(form.title, form.content);
       }
+      toast.success(editingId ? '공지사항이 수정되었습니다.' : '공지사항이 등록되었습니다.');
       setForm({ title: '', content: '' });
       setEditingId(null);
       load();
     } catch (err) {
-      setError(err.message || '처리에 실패했습니다.');
+      toast.error(err.message || '처리에 실패했습니다.');
     } finally {
       setLoading(false);
     }
@@ -50,9 +60,10 @@ export default function AnnouncementAdmin() {
     if (!confirm('삭제하시겠습니까?')) return;
     try {
       await deleteAnnouncement(id);
+      toast.success('공지사항이 삭제되었습니다.');
       load();
     } catch (err) {
-      setError(err.message || '삭제에 실패했습니다.');
+      toast.error(err.message || '삭제에 실패했습니다.');
     }
   };
 
@@ -62,6 +73,25 @@ export default function AnnouncementAdmin() {
     setError('');
   };
 
+  if (fetchLoading) {
+    return (
+      <div className="admin-section">
+        <h2 className="admin-section-title">공지사항 관리</h2>
+        <p className="admin-loading">불러오는 중...</p>
+      </div>
+    );
+  }
+
+  if (fetchError) {
+    return (
+      <div className="admin-section">
+        <h2 className="admin-section-title">공지사항 관리</h2>
+        <p className="admin-error">{fetchError}</p>
+        <button className="btn-admin-secondary" onClick={load}>다시 시도</button>
+      </div>
+    );
+  }
+
   return (
     <div className="admin-section">
       <h2 className="admin-section-title">공지사항 관리</h2>

src/components/admin/DownloadAdmin.jsx

@@ -141,13 +141,40 @@ function UploadForm({ title, hint, accept, endpoint, onSuccess }) {
 
 export default function DownloadAdmin() {
   const [info, setInfo] = useState(null);
+  const [loading, setLoading] = useState(true);
+  const [loadError, setLoadError] = useState('');
 
   useEffect(() => {
-    getDownloadInfo().then(setInfo).catch((err) => {
+    getDownloadInfo()
+      .then((data) => {
+        setInfo(data);
+        setLoadError('');
+      })
+      .catch((err) => {
         console.error('다운로드 정보 로드 실패:', err);
-    });
+        setLoadError('배포 정보를 불러올 수 없습니다.');
+      })
+      .finally(() => setLoading(false));
   }, []);
 
+  if (loading) {
+    return (
+      <div className="admin-section">
+        <h2 className="admin-section-title">게임 배포 관리</h2>
+        <p className="admin-loading">불러오는 중...</p>
+      </div>
+    );
+  }
+
+  if (loadError) {
+    return (
+      <div className="admin-section">
+        <h2 className="admin-section-title">게임 배포 관리</h2>
+        <p className="admin-error">{loadError}</p>
+      </div>
+    );
+  }
+
   return (
     <div className="admin-section">
       <h2 className="admin-section-title">게임 배포 관리</h2>

src/components/admin/UserAdmin.jsx

@@ -1,6 +1,7 @@
 import { useState, useEffect, useCallback } from 'react';
 import { getUsers, updateUserRole, deleteUser } from '../../api/users';
 import { useAuth } from '../../context/useAuth';
+import { useToast } from '../toast/useToast';
 import './AdminCommon.css';
 
 export default function UserAdmin() {
@@ -8,6 +9,7 @@ export default function UserAdmin() {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState('');
   const { user: me } = useAuth();
+  const toast = useToast();
 
   const load = useCallback(() => {
     getUsers()
@@ -23,9 +25,10 @@ export default function UserAdmin() {
     setError('');
     try {
       await updateUserRole(u.id, newRole);
+      toast.success(`${u.username}의 권한이 ${newRole}로 변경되었습니다.`);
       load();
     } catch (err) {
-      setError(err.message || '권한 변경에 실패했습니다.');
+      toast.error(err.message || '권한 변경에 실패했습니다.');
     }
   };
 
@@ -34,9 +37,10 @@ export default function UserAdmin() {
     setError('');
     try {
       await deleteUser(u.id);
+      toast.success(`${u.username} 계정이 삭제되었습니다.`);
       load();
     } catch (err) {
-      setError(err.message || '삭제에 실패했습니다.');
+      toast.error(err.message || '삭제에 실패했습니다.');
     }
   };
 

src/components/toast/ToastProvider.jsx

@@ -0,0 +1,70 @@
+import { useState, useCallback, useRef } from 'react';
+import { ToastContext } from './toastContextValue';
+
+let toastId = 0;
+
+export function ToastProvider({ children }) {
+  const [toasts, setToasts] = useState([]);
+  const timersRef = useRef({});
+
+  const removeToast = useCallback((id) => {
+    clearTimeout(timersRef.current[id]);
+    delete timersRef.current[id];
+    setToasts((prev) => prev.filter((t) => t.id !== id));
+  }, []);
+
+  const addToast = useCallback((message, type = 'info', duration = 3000) => {
+    const id = ++toastId;
+    setToasts((prev) => [...prev, { id, message, type }]);
+    timersRef.current[id] = setTimeout(() => removeToast(id), duration);
+    return id;
+  }, [removeToast]);
+
+  const toast = useCallback((message) => addToast(message, 'info'), [addToast]);
+  toast.success = useCallback((message) => addToast(message, 'success'), [addToast]);
+  toast.error = useCallback((message) => addToast(message, 'error'), [addToast]);
+  toast.warn = useCallback((message) => addToast(message, 'warn'), [addToast]);
+
+  return (
+    <ToastContext.Provider value={toast}>
+      {children}
+      <div style={containerStyle}>
+        {toasts.map((t) => (
+          <div key={t.id} style={{ ...itemStyle, ...typeStyles[t.type] }} onClick={() => removeToast(t.id)}>
+            {t.message}
+          </div>
+        ))}
+      </div>
+    </ToastContext.Provider>
+  );
+}
+
+const containerStyle = {
+  position: 'fixed',
+  top: 16,
+  right: 16,
+  zIndex: 10000,
+  display: 'flex',
+  flexDirection: 'column',
+  gap: 8,
+  pointerEvents: 'none',
+};
+
+const itemStyle = {
+  padding: '12px 20px',
+  borderRadius: 8,
+  color: '#fff',
+  fontSize: 14,
+  maxWidth: 360,
+  cursor: 'pointer',
+  pointerEvents: 'auto',
+  boxShadow: '0 4px 12px rgba(0,0,0,0.3)',
+  animation: 'toast-in 0.25s ease-out',
+};
+
+const typeStyles = {
+  info: { backgroundColor: '#3a3a3a' },
+  success: { backgroundColor: '#2d6a4f' },
+  error: { backgroundColor: '#9b2226' },
+  warn: { backgroundColor: '#7f5539' },
+};

src/components/toast/toastContextValue.js

@@ -0,0 +1,3 @@
+import { createContext } from 'react';
+
+export const ToastContext = createContext(null);

src/components/toast/useToast.js

@@ -0,0 +1,8 @@
+import { useContext } from 'react';
+import { ToastContext } from './toastContextValue';
+
+export function useToast() {
+  const ctx = useContext(ToastContext);
+  if (!ctx) throw new Error('useToast must be used within ToastProvider');
+  return ctx;
+}

src/index.css

@@ -31,3 +31,14 @@ a {
 a:hover {
   opacity: 0.85;
 }
+
+@keyframes toast-in {
+  from {
+    opacity: 0;
+    transform: translateX(40px);
+  }
+  to {
+    opacity: 1;
+    transform: translateX(0);
+  }
+}