Webhook URL 형식 검증 로직 분리 및 재사용성 개선:

- WebhookUrlValidator 추가: URL 형식 검증 전담
- Service/Controller에서 공통 Validator 활용하도록 수정

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

@@ -25733,29 +25733,31 @@ input[type=checkbox]:checked + .custom-checkbox {
   padding: 24px 16px 60px;
   font-family: "Spoqa Han Sans Neo", "Noto Sans CJK KR", sans-serif;
 }
-.webhook-container .field-help {
+
+.step1-wrap .field-help {
   color: #64748b;
   font-size: 13px;
   margin-top: 6px;
 }
-.webhook-container .field-help-red {
+.step1-wrap .field-help-red {
   color: #f4253c;
   font-size: 13px;
   margin-top: 6px;
   font-weight: 500;
 }
 @media (max-width: 768px) {
-  .webhook-container .field-help-red {
+  .step1-wrap .field-help-red {
     font-size: 11px;
   }
 }
-.webhook-container .field-error,
-.webhook-container .webhook-field-error {
+.step1-wrap .field-error,
+.step1-wrap .webhook-field-error {
   color: #f4253c;
   font-size: 13px;
+  font-weight: 600;
   margin-top: 6px;
 }
-.webhook-container .req {
+.step1-wrap .req {
   color: #f4253c;
 }