fix(audit): origin_domain 추출 시 Referer 헤더 fallback 추가

same-origin 요청(guide→guide)은 Origin 헤더가 없으므로
Referer 헤더에서 도메인을 추출하도록 fallback 로직 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/java/com/gcsc/guide/config/ApiAccessLogInterceptor.java

@@ -49,7 +49,8 @@ public class ApiAccessLogInterceptor implements HandlerInterceptor {
                 }
             }
 
-            String originDomain = extractOriginDomain(request.getHeader("Origin"));
+            String originDomain = resolveOriginDomain(
+                request.getHeader("Origin"), request.getHeader("Referer"));
 
             String queryString = request.getQueryString();
             if (queryString != null && queryString.length() > 2000) {
@@ -75,14 +76,15 @@ public class ApiAccessLogInterceptor implements HandlerInterceptor {
         }
     }
 
-    private String extractOriginDomain(String origin) {
-        if (origin == null || origin.isBlank()) {
+    private String resolveOriginDomain(String origin, String referer) {
+        String url = (origin != null && !origin.isBlank()) ? origin : referer;
+        if (url == null || url.isBlank()) {
             return null;
         }
         try {
-            return URI.create(origin).getHost();
+            return URI.create(url).getHost();
         } catch (Exception e) {
-            return origin;
+            return null;
         }
     }
 }