[feat]: 회원가입 페이지 개선 및 폼 자동 포맷팅 기능 추가

주요 변경사항:
- 회원가입 폼에 사업자등록번호 자동 포맷팅 (000-00-00000)
- 핸드폰 번호 자동 포맷팅 (010-1111-1111 / 010-111-1111)
- 약관 전체 동의 체크박스 추가 및 개별 약관 연동
- 모든 입력 필드에 autocomplete 속성 추가 (브라우저 자동완성 지원)
- 회원가입 API 연동 및 백엔드 통신 구현
- LoginPage 폼 태그 추가 및 DOM 경고 수정
- LanguageSelect 언어 변경 시 전체 페이지 새로고침으로 변경
- 다국어 번역 키 추가 (ko, en, ja)

🤖 Generated with Claude Code

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

src/app/api/auth/login/route.ts

@@ -23,7 +23,7 @@ export async function POST(request: NextRequest) {
     }
 
     // Call PHP backend API
-    const response = await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/v1/login`, {
+    const backendResponse = await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/v1/login`, {
       method: 'POST',
       headers: {
         'Content-Type': 'application/json',
@@ -33,18 +33,26 @@ export async function POST(request: NextRequest) {
       body: JSON.stringify({ user_id, user_pwd }),
     });
 
-    if (!response.ok) {
-      const errorData = await response.json().catch(() => ({}));
+    if (!backendResponse.ok) {
+      // Don't expose detailed backend error messages to client
+      // Use generic error messages based on status code
+      let errorMessage = 'Authentication failed';
+
+      if (backendResponse.status === 422) {
+        errorMessage = 'Invalid credentials provided';
+      } else if (backendResponse.status === 429) {
+        errorMessage = 'Too many login attempts. Please try again later';
+      } else if (backendResponse.status >= 500) {
+        errorMessage = 'Service temporarily unavailable';
+      }
+
       return NextResponse.json(
-        {
-          error: errorData.message || 'Login failed',
-          status: response.status
-        },
-        { status: response.status }
+        { error: errorMessage },
+        { status: backendResponse.status === 422 ? 401 : backendResponse.status }
       );
     }
 
-    const data = await response.json();
+    const data = await backendResponse.json();
 
     // Prepare response with user data (no token exposed)
     const responseData = {
@@ -52,26 +60,38 @@ export async function POST(request: NextRequest) {
       user: data.user,
       tenant: data.tenant,
       menus: data.menus,
+      token_type: data.token_type,
+      expires_in: data.expires_in,
+      expires_at: data.expires_at,
     };
 
-    // Set HttpOnly cookie with token
-    const cookieOptions = [
-      `user_token=${data.user_token}`,
+    // Set HttpOnly cookies for both access_token and refresh_token
+    const accessTokenCookie = [
+      `access_token=${data.access_token}`,
       'HttpOnly',              // ✅ JavaScript cannot access
       'Secure',                // ✅ HTTPS only (production)
       'SameSite=Strict',       // ✅ CSRF protection
       'Path=/',
-      'Max-Age=604800',        // 7 days
+      `Max-Age=${data.expires_in || 7200}`, // Use backend expiry (default 2 hours)
     ].join('; ');
 
-    console.log('✅ Login successful - Token stored in HttpOnly cookie');
+    const refreshTokenCookie = [
+      `refresh_token=${data.refresh_token}`,
+      'HttpOnly',              // ✅ JavaScript cannot access
+      'Secure',                // ✅ HTTPS only (production)
+      'SameSite=Strict',       // ✅ CSRF protection
+      'Path=/',
+      'Max-Age=604800',        // 7 days (longer for refresh token)
+    ].join('; ');
 
-    return NextResponse.json(responseData, {
-      status: 200,
-      headers: {
-        'Set-Cookie': cookieOptions,
-      },
-    });
+    console.log('✅ Login successful - Access & Refresh tokens stored in HttpOnly cookies');
+
+    const response = NextResponse.json(responseData, { status: 200 });
+
+    response.headers.append('Set-Cookie', accessTokenCookie);
+    response.headers.append('Set-Cookie', refreshTokenCookie);
+
+    return response;
 
   } catch (error) {
     console.error('Login proxy error:', error);