Fix author URL saving issue in multipart form submission

Changed frontend to send multiple URL parameters with same name ('urls')
instead of indexed parameters ('urls[0]', 'urls[1]'). Spring Boot expects
list parameters in multipart forms to use the same parameter name, not
array-style indexed naming.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

frontend/src/app/authors/[id]/edit/page.tsx

@@ -132,10 +132,10 @@ export default function EditAuthorPage() {
         updateFormData.append('authorRating', formData.authorRating.toString());
       }
       
-      // Add URLs as array
+      // Add URLs as multiple parameters with same name
       const validUrls = formData.urls.filter(url => url.trim());
-      validUrls.forEach((url, index) => {
-        updateFormData.append(`urls[${index}]`, url);
+      validUrls.forEach((url) => {
+        updateFormData.append('urls', url);
       });
 
       // Add avatar if selected