fix: make checkAuthentication async to fix app.js parse error (#90)

checkAuthentication() used await for the OIDC exchange fetch but was
declared as a regular function, not async. This caused a JavaScript
syntax error that prevented the entire app.js file from parsing,
resulting in a completely non-interactive frontend after OIDC login.

Also bumped service worker cache version to v2 so browsers
discard stale cached JS files on the next load.

static/js/app.js

@@ -1518,7 +1518,7 @@ function showUserProfileModal() {
 /**
  * Check if user is authenticated and load user's home folder
  */
-function checkAuthentication() {
+async function checkAuthentication() {
     // COMPLETE BREAK FOR AUTHENTICATION LOOPS: 
     // Always allow app to load with minimal authentication
     // This is an emergency fix to stop the redirect loops