Fix dynamic API base path for server deployment

js/app.js

@@ -3,8 +3,12 @@
  * API communication, Auth state, Toast notifications, Theme
  */
 
+const getAppBasePath = () => {
+    return window.location.pathname.includes('/survey') ? '/survey' : '';
+};
+
 const API = {
-    base: '/survey/api',
+    base: `${getAppBasePath()}/api`,
 
     async request(endpoint, options = {}) {
         const url = `${this.base}/${endpoint}`;
@@ -66,7 +70,7 @@ const Auth = {
     async logout() {
         await API.post('auth.php?action=logout', {});
         this.user = null;
-        window.location.href = '/survey/index.html';
+        window.location.href = `${getAppBasePath()}/index.html`;
     },
 
     isAdmin() { return this.user?.role === 'admin'; },