[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/lib/auth/token-refresh.ts

@@ -0,0 +1,96 @@
+/**
+ * Token Refresh Utility
+ *
+ * Handles automatic token refresh logic for client and server
+ */
+
+/**
+ * Client-side token refresh
+ * Call this when you receive 401 errors from protected API calls
+ */
+export async function refreshTokenClient(): Promise<boolean> {
+  try {
+    const response = await fetch('/api/auth/refresh', {
+      method: 'POST',
+      credentials: 'include', // Include HttpOnly cookies
+    });
+
+    if (!response.ok) {
+      const data = await response.json();
+
+      // If refresh failed and needs re-authentication
+      if (data.needsReauth) {
+        console.warn('🔄 Token refresh failed - redirecting to login');
+        window.location.href = '/login';
+        return false;
+      }
+
+      return false;
+    }
+
+    console.log('✅ Token refreshed successfully');
+    return true;
+
+  } catch (error) {
+    console.error('❌ Token refresh error:', error);
+    return false;
+  }
+}
+
+/**
+ * Server-side token refresh (for API routes and middleware)
+ */
+export async function refreshTokenServer(refreshToken: string): Promise<{
+  success: boolean;
+  accessToken?: string;
+  newRefreshToken?: string;
+  expiresIn?: number;
+}> {
+  try {
+    const response = await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/v1/refresh`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Accept': 'application/json',
+        'Authorization': `Bearer ${refreshToken}`,
+        'X-API-KEY': process.env.NEXT_PUBLIC_API_KEY || '',
+      },
+    });
+
+    if (!response.ok) {
+      return { success: false };
+    }
+
+    const data = await response.json();
+
+    return {
+      success: true,
+      accessToken: data.access_token,
+      newRefreshToken: data.refresh_token,
+      expiresIn: data.expires_in,
+    };
+
+  } catch (error) {
+    console.error('Token refresh error:', error);
+    return { success: false };
+  }
+}
+
+/**
+ * Check if token is expired or about to expire (within 5 minutes)
+ * @param expiresAt - Expiration timestamp from backend (e.g., "2025-11-10 15:49:38")
+ */
+export function shouldRefreshToken(expiresAt: string | null): boolean {
+  if (!expiresAt) return true; // If no expiration info, assume expired
+
+  try {
+    const expiryTime = new Date(expiresAt).getTime();
+    const currentTime = Date.now();
+    const fiveMinutes = 5 * 60 * 1000; // 5 minutes in milliseconds
+
+    // Refresh if token expires in less than 5 minutes
+    return (expiryTime - currentTime) < fiveMinutes;
+  } catch {
+    return true; // If parsing fails, assume expired
+  }
+}