Add URL converter link to popup menu

A new link to the URL converter (https://xuc.xi-xu.me/) has been added to the popup menu for easier access.

popup.html

@@ -570,6 +570,10 @@
             <span class="link-icon">📖</span>
             <span class="link-text">扩展存储库</span>
           </a>
+          <a href="https://xuc.xi-xu.me/" target="_blank" class="link-item">
+            <span class="link-icon">🔗</span>
+            <span class="link-text">URL 转换器</span>
+          </a>
         </div>
       </div>