feat: 회원가입 페이지 및 API 추가

- RegisterPage 추가 (아이디/비밀번호/비밀번호 확인 폼, 클라이언트 유효성 검사)
- /register 라우트 추가 (로그인 상태 시 홈 리다이렉트)
- 로그인 페이지에 회원가입 링크 및 가입 완료 안내 메시지 추가
- api/auth.js에 register() 함수 추가

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.jsx

@@ -1,6 +1,7 @@
 import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom';
 import { AuthProvider, useAuth } from './context/AuthContext';
 import LoginPage from './pages/LoginPage';
+import RegisterPage from './pages/RegisterPage';
 import HomePage from './pages/HomePage';
 import AdminPage from './pages/AdminPage';
 
@@ -16,6 +17,7 @@ function AppRoutes() {
   return (
     <Routes>
       <Route path="/login" element={user ? <Navigate to="/" replace /> : <LoginPage />} />
+      <Route path="/register" element={user ? <Navigate to="/" replace /> : <RegisterPage />} />
       <Route path="/" element={<HomePage />} />
       <Route
         path="/admin"

src/api/auth.js

@@ -6,3 +6,10 @@ export async function login(username, password) {
     body: JSON.stringify({ username, password }),
   });
 }
+
+export async function register(username, password) {
+  return apiFetch('/api/auth/register', {
+    method: 'POST',
+    body: JSON.stringify({ username, password }),
+  });
+}

src/pages/LoginPage.css

@@ -77,6 +77,13 @@
   border-color: #BACDB0;
 }
 
+.login-success {
+  color: #81c784;
+  font-size: 0.85rem;
+  margin: 0;
+  text-align: center;
+}
+
 .login-error {
   color: #e57373;
   font-size: 0.85rem;

src/pages/LoginPage.jsx

@@ -1,5 +1,5 @@
 import { useState } from 'react';
-import { useNavigate, Link } from 'react-router-dom';
+import { useNavigate, Link, useLocation } from 'react-router-dom';
 import { useAuth } from '../context/AuthContext';
 import './LoginPage.css';
 
@@ -10,6 +10,8 @@ export default function LoginPage() {
   const [loading, setLoading] = useState(false);
   const { login } = useAuth();
   const navigate = useNavigate();
+  const location = useLocation();
+  const justRegistered = location.state?.registered;
 
   const handleSubmit = async (e) => {
     e.preventDefault();
@@ -58,6 +60,7 @@ export default function LoginPage() {
             />
           </div>
 
+          {justRegistered && <p className="login-success">회원가입이 완료되었습니다. 로그인해주세요.</p>}
           {error && <p className="login-error">{error}</p>}
 
           <button type="submit" className="btn-login" disabled={loading}>
@@ -77,6 +80,7 @@ export default function LoginPage() {
           SSAFY 계정으로 로그인
         </button>
 
+        <Link to="/register" className="login-back">계정이 없으신가요? 회원가입</Link>
         <Link to="/" className="login-back">메인으로 돌아가기</Link>
       </div>
     </div>

src/pages/RegisterPage.jsx

@@ -0,0 +1,94 @@
+import { useState } from 'react';
+import { useNavigate, Link } from 'react-router-dom';
+import { register } from '../api/auth';
+import './LoginPage.css';
+
+export default function RegisterPage() {
+  const [username, setUsername] = useState('');
+  const [password, setPassword] = useState('');
+  const [confirm, setConfirm] = useState('');
+  const [error, setError] = useState('');
+  const [loading, setLoading] = useState(false);
+  const navigate = useNavigate();
+
+  const handleSubmit = async (e) => {
+    e.preventDefault();
+    setError('');
+
+    if (password !== confirm) {
+      setError('비밀번호가 일치하지 않습니다.');
+      return;
+    }
+    if (password.length < 6) {
+      setError('비밀번호는 6자 이상이어야 합니다.');
+      return;
+    }
+
+    setLoading(true);
+    try {
+      await register(username, password);
+      navigate('/login', { state: { registered: true } });
+    } catch (err) {
+      setError(err.message || '회원가입에 실패했습니다.');
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  return (
+    <div className="login-page">
+      <div className="login-panel">
+        <div className="login-header">
+          <h1 className="game-title">A301</h1>
+          <p className="game-subtitle">MULTIPLAYER</p>
+        </div>
+
+        <form className="login-form" onSubmit={handleSubmit}>
+          <div className="input-group">
+            <label htmlFor="username">아이디</label>
+            <input
+              id="username"
+              type="text"
+              value={username}
+              onChange={(e) => setUsername(e.target.value)}
+              placeholder="아이디를 입력하세요"
+              autoComplete="username"
+            />
+          </div>
+
+          <div className="input-group">
+            <label htmlFor="password">비밀번호</label>
+            <input
+              id="password"
+              type="password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              placeholder="6자 이상 입력하세요"
+              autoComplete="new-password"
+            />
+          </div>
+
+          <div className="input-group">
+            <label htmlFor="confirm">비밀번호 확인</label>
+            <input
+              id="confirm"
+              type="password"
+              value={confirm}
+              onChange={(e) => setConfirm(e.target.value)}
+              placeholder="비밀번호를 다시 입력하세요"
+              autoComplete="new-password"
+            />
+          </div>
+
+          {error && <p className="login-error">{error}</p>}
+
+          <button type="submit" className="btn-login" disabled={loading}>
+            {loading ? '처리 중...' : '회원가입'}
+          </button>
+        </form>
+
+        <Link to="/login" className="login-back">이미 계정이 있으신가요? 로그인</Link>
+      </div>
+    </div>
+  );
+}