fix: Implement Network-First SW strategy, no-cache headers in Nginx for index.html/sw.js, and auto 401 token cleanup to fix post-redeploy stale cache issues

frontend/index.html

@@ -19,7 +19,9 @@
     <script>
       if ('serviceWorker' in navigator) {
         window.addEventListener('load', () => {
-          navigator.serviceWorker.register('/sw.js').catch(err => console.log('SW reg error:', err));
+          navigator.serviceWorker.register('/sw.js').then(reg => {
+            reg.update();
+          }).catch(err => console.log('SW reg error:', err));
         });
       }
     </script>