2FA (추가 인증) 기능 추가:

- Step-up 인증 Interceptor 및 보호 경로 관리 로직 도입
- 2FA 팝업 모듈 및 스타일(SASS, JS) 추가
- 로그인 실패 사유 Enum 및 2FA 관련 처리 로직 공통화

src/main/resources/static/css/main.css

@@ -711,75 +711,6 @@ hr {
   --transition-smooth: all 0.4s cubic-bezier(0.16, 1, 0.3, 1);
 }
 
-.design-survey-bar {
-  position: fixed;
-  top: 0;
-  left: 0;
-  right: 0;
-  height: 48px;
-  background: linear-gradient(90deg, #667eea 0%, #764ba2 100%);
-  z-index: 400;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
-}
-.design-survey-bar .survey-container {
-  display: flex;
-  align-items: center;
-  gap: 16px;
-}
-.design-survey-bar .survey-label {
-  color: #ffffff;
-  font-size: 14px;
-  font-weight: 500;
-}
-.design-survey-bar .survey-buttons {
-  display: flex;
-  gap: 8px;
-}
-.design-survey-bar .survey-btn {
-  padding: 6px 16px;
-  border: 2px solid rgba(255, 255, 255, 0.5);
-  border-radius: 20px;
-  background: transparent;
-  color: #ffffff;
-  font-size: 14px;
-  font-weight: 600;
-  cursor: pointer;
-  transition: all 0.3s ease;
-}
-.design-survey-bar .survey-btn:hover {
-  background: rgba(255, 255, 255, 0.2);
-  border-color: #ffffff;
-}
-.design-survey-bar .survey-btn.active {
-  background: #ffffff;
-  color: #667eea;
-  border-color: #ffffff;
-}
-@media (max-width: 768px) {
-  .design-survey-bar {
-    height: 40px;
-  }
-  .design-survey-bar .survey-label {
-    display: none;
-  }
-  .design-survey-bar .survey-btn {
-    padding: 4px 12px;
-    font-size: 12px;
-  }
-}
-
-body.design-survey-active .global-header {
-  margin-top: 48px;
-}
-@media (max-width: 768px) {
-  body.design-survey-active .global-header {
-    margin-top: 40px;
-  }
-}
-
 .blind {
   position: absolute;
   width: 1px;
@@ -7634,6 +7565,123 @@ button.djb-comment-submit:disabled {
   color: #888;
 }
 
+#tfaModal .modal-title {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.tfa-subtitle {
+  text-align: center;
+  color: #64748B;
+  margin-bottom: 24px;
+  font-size: 14px;
+}
+
+.tfa-segment {
+  display: flex;
+  gap: 8px;
+  margin-bottom: 20px;
+}
+.tfa-segment .tfa-seg-btn {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 4px;
+  padding: 12px 8px;
+  border: 1px solid #CBD5E1;
+  border-radius: 8px;
+  background: #F8FAFC;
+  color: #475569;
+  font-size: 14px;
+  font-weight: 600;
+  cursor: pointer;
+  transition: all 0.15s ease;
+}
+.tfa-segment .tfa-seg-btn:hover {
+  border-color: #0049B4;
+}
+.tfa-segment .tfa-seg-btn.is-active {
+  background: #0049B4;
+  border-color: #0049B4;
+  color: #FFFFFF;
+}
+.tfa-segment .tfa-seg-btn.is-active .tfa-seg-masked {
+  color: rgba(255, 255, 255, 0.85);
+}
+.tfa-segment .tfa-seg-masked {
+  font-size: 12px;
+  font-weight: 400;
+  color: #94A3B8;
+}
+
+.tfa-btn-block {
+  width: 100%;
+  margin-top: 8px;
+}
+
+.tfa-code-row {
+  position: relative;
+  display: flex;
+  align-items: center;
+}
+.tfa-code-row .tfa-code-input {
+  width: 100%;
+  padding: 14px 64px 14px 16px;
+  border: 1px solid #CBD5E1;
+  border-radius: 8px;
+  font-size: 15px;
+  letter-spacing: 2px;
+}
+.tfa-code-row .tfa-code-input:focus {
+  outline: none;
+  border-color: #0049B4;
+}
+.tfa-code-row .tfa-timer {
+  position: absolute;
+  right: 16px;
+  color: #E11D48;
+  font-size: 14px;
+  font-weight: 600;
+  font-variant-numeric: tabular-nums;
+}
+
+.tfa-message {
+  min-height: 18px;
+  margin-top: 8px;
+  font-size: 13px;
+  color: #64748B;
+}
+.tfa-message.is-error {
+  color: #E11D48;
+}
+
+.tfa-test-notice {
+  margin-top: 8px;
+  padding: 10px 14px;
+  border: 1px dashed #F59E0B;
+  border-radius: 8px;
+  background: #FFFBEB;
+  color: #B45309;
+  font-size: 13px;
+  text-align: center;
+}
+
+.tfa-actions {
+  display: flex;
+  justify-content: flex-end;
+  margin: 8px 0;
+}
+.tfa-actions .tfa-resend {
+  background: none;
+  border: none;
+  color: #0049B4;
+  font-size: 13px;
+  cursor: pointer;
+  text-decoration: underline;
+}
+
 .hero-carousel-section {
   position: relative;
   width: 100%;