✨ 회원가입 신청 기능 완성 (간소화)

백엔드:
- signup_routes.py 신규 생성
- POST /auth/signup-request: 회원가입 신청
- GET /auth/signup-requests: 승인 대기 목록 (관리자)
- POST /auth/approve-signup/{id}: 승인 (관리자)
- DELETE /auth/reject-signup/{id}: 거부 (관리자)
- main.py에 signup_router 등록

프론트엔드:
- SimpleLogin에 회원가입 폼 추가
- 필수 항목만: 사용자명, 비밀번호, 비밀번호 확인, 이름
- 간단하고 깔끔한 UI
- 비밀번호 일치 검사 및 최소 길이 검사
- 제출 후 승인 대기 안내 메시지

frontend/src/SimpleLogin.jsx

@@ -9,6 +9,18 @@ const SimpleLogin = ({ onLoginSuccess }) => {
     const [isLoading, setIsLoading] = useState(false);
     const [error, setError] = useState('');
     const [success, setSuccess] = useState('');
+    const [showSignup, setShowSignup] = useState(false);
+    const [signupData, setSignupData] = useState({
+        username: '',
+        password: '',
+        confirmPassword: '',
+        name: '',
+        email: '',
+        department: '',
+        position: '',
+        phone: '',
+        reason: ''
+    });
 
     const handleChange = (e) => {
         const { name, value } = e.target;
@@ -19,6 +31,73 @@ const SimpleLogin = ({ onLoginSuccess }) => {
         if (error) setError('');
     };
 
+    const handleSignupChange = (e) => {
+        const { name, value } = e.target;
+        setSignupData(prev => ({
+            ...prev,
+            [name]: value
+        }));
+        if (error) setError('');
+    };
+
+    const handleSignupSubmit = async (e) => {
+        e.preventDefault();
+        
+        // 유효성 검사
+        if (!signupData.username || !signupData.password || !signupData.name) {
+            setError('필수 항목을 모두 입력해주세요.');
+            return;
+        }
+        
+        if (signupData.password !== signupData.confirmPassword) {
+            setError('비밀번호가 일치하지 않습니다.');
+            return;
+        }
+        
+        if (signupData.password.length < 6) {
+            setError('비밀번호는 최소 6자 이상이어야 합니다.');
+            return;
+        }
+        
+        setIsLoading(true);
+        setError('');
+        
+        try {
+            const response = await api.post('/auth/signup-request', {
+                username: signupData.username,
+                password: signupData.password,
+                name: signupData.name,
+                email: signupData.email || null,
+                department: signupData.department || null,
+                position: signupData.position || null,
+                phone: signupData.phone || null,
+                reason: signupData.reason || null
+            });
+            
+            if (response.data.success) {
+                setSuccess('회원가입 요청이 전송되었습니다. 관리자 승인 후 이용 가능합니다.');
+                setShowSignup(false);
+                // 폼 초기화
+                setSignupData({
+                    username: '',
+                    password: '',
+                    confirmPassword: '',
+                    name: '',
+                    email: '',
+                    department: '',
+                    position: '',
+                    phone: '',
+                    reason: ''
+                });
+            }
+        } catch (err) {
+            const errorMsg = err.response?.data?.detail || '회원가입 요청 중 오류가 발생했습니다.';
+            setError(errorMsg);
+        } finally {
+            setIsLoading(false);
+        }
+    };
+
     const handleSubmit = async (e) => {
         e.preventDefault();
         
@@ -175,6 +254,55 @@ const SimpleLogin = ({ onLoginSuccess }) => {
                         {isLoading ? '로그인 중...' : '로그인'}
                     </button>
                 </form>
+                
+                {/* 회원가입 버튼 */}
+                <div style={{ marginTop: '20px', textAlign: 'center' }}>
+                    <button
+                        type="button"
+                        onClick={() => {
+                            setShowSignup(!showSignup);
+                            setError('');
+                            setSuccess('');
+                        }}
+                        style={{
+                            width: '100%',
+                            padding: '14px',
+                            backgroundColor: showSignup ? '#6b7280' : '#10b981',
+                            color: 'white',
+                            border: 'none',
+                            borderRadius: '8px',
+                            fontSize: '16px',
+                            fontWeight: '600',
+                            cursor: 'pointer',
+                            transition: 'background-color 0.3s ease'
+                        }}
+                    >
+                        {showSignup ? '✕ 닫기' : '➕ 회원가입 신청'}
+                    </button>
+                </div>
+                
+                {/* 회원가입 폼 */}
+                {showSignup && (
+                    <div style={{
+                        marginTop: '20px',
+                        padding: '20px',
+                        background: '#f0fdf4',
+                        border: '2px solid #10b981',
+                        borderRadius: '12px',
+                        maxHeight: '500px',
+                        overflowY: 'auto'
+                    }}>
+                        <form onSubmit={handleSignupSubmit} style={{ display: 'flex', flexDirection: 'column', gap: '14px' }}>
+                            <input type="text" name="username" value={signupData.username} onChange={handleSignupChange} placeholder="사용자명*" required style={{ padding: '12px', border: '1px solid #d1d5db', borderRadius: '6px', fontSize: '14px' }} />
+                            <input type="password" name="password" value={signupData.password} onChange={handleSignupChange} placeholder="비밀번호 (최소 6자)*" required style={{ padding: '12px', border: '1px solid #d1d5db', borderRadius: '6px', fontSize: '14px' }} />
+                            <input type="password" name="confirmPassword" value={signupData.confirmPassword} onChange={handleSignupChange} placeholder="비밀번호 확인*" required style={{ padding: '12px', border: '1px solid #d1d5db', borderRadius: '6px', fontSize: '14px' }} />
+                            <input type="text" name="name" value={signupData.name} onChange={handleSignupChange} placeholder="이름*" required style={{ padding: '12px', border: '1px solid #d1d5db', borderRadius: '6px', fontSize: '14px' }} />
+                            <button type="submit" disabled={isLoading} style={{ padding: '14px', background: isLoading ? '#9ca3af' : '#10b981', color: 'white', border: 'none', borderRadius: '8px', fontSize: '16px', fontWeight: '600', cursor: isLoading ? 'not-allowed' : 'pointer', marginTop: '8px' }}>
+                                {isLoading ? '처리 중...' : '✓ 회원가입 신청'}
+                            </button>
+                        </form>
+                    </div>
+                )}
 
                 {error && (
                     <div style={{