feat: add Progressive Web App support with service worker and offline functionality

src/js/app.js

@@ -1,5 +1,23 @@
 // Application initialization and event handlers
 
+// Register service worker for PWA functionality
+if ('serviceWorker' in navigator) {
+    window.addEventListener('load', () => {
+        navigator.serviceWorker.register('/sw.js')
+            .then(registration => {
+                console.log('Service Worker registered:', registration.scope);
+
+                // Check for updates periodically
+                setInterval(() => {
+                    registration.update();
+                }, 60000); // Check every minute
+            })
+            .catch(error => {
+                console.warn('Service Worker registration failed:', error);
+            });
+    });
+}
+
 document.addEventListener('DOMContentLoaded', function () {
     // Initialize user settings
     initSettings();