[Feature] UI - Leftnav: Add external link icon to Learning Resources

Add ExportOutlined icon next to nav items that link to external pages,
making it clear to users when a link opens in a new tab.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/litellm-dashboard/src/components/leftnav.tsx

@@ -13,6 +13,7 @@ import {
   CreditCardOutlined,
   DatabaseOutlined,
   ExperimentOutlined,
+  ExportOutlined,
   FileTextOutlined,
   FolderOutlined,
   KeyOutlined,
@@ -400,7 +401,7 @@ const Sidebar: React.FC<SidebarProps> = ({ setPage, defaultSelectedKey, collapse
           onClick={(e) => e.stopPropagation()}
           style={{ color: "inherit", textDecoration: "none" }}
         >
-          {label}
+          {label} <ExportOutlined style={{ fontSize: 10, marginLeft: 4 }} />
         </a>
       );
     }