unify the prod and dev env and use only relative base path ./ in the Admin UI

ui/index.html

@@ -27,6 +27,6 @@
 </head>
 <body>
     <div id="app"></div>
-    <script type="module" src="/src/main.js"></script>
+    <script type="module" src="./src/main.js"></script>
 </body>
 </html>