Remove manual service worker registration; rely on VitePWA auto-registration

- Deleted src/registerServiceWorker.ts and all related imports
- Cleaned up WebPlatformService and main.web.ts to remove manual SW logic
- Updated VitePWA config for correct dev/prod SW handling
- Fixed missing FontAwesome download icon in PWA prompt
- Updated docs to reflect new PWA registration approach

PWA now works reliably in all web environments with zero manual SW code.

src/components/PWAInstallPrompt.vue

@@ -79,12 +79,6 @@ export default class PWAInstallPrompt extends Vue {
   }
 
   private setupInstallPrompt() {
-    // Only show install prompt if PWA is enabled
-    if (process.env.VITE_PWA_ENABLED !== "true") {
-      logger.debug("[PWA] Install prompt disabled - PWA not enabled");
-      return;
-    }
-
     // Check if already installed
     if (this.isPWAInstalled()) {
       logger.debug("[PWA] Install prompt disabled - PWA already installed");
@@ -95,9 +89,6 @@ export default class PWAInstallPrompt extends Vue {
     window.addEventListener('beforeinstallprompt', (e) => {
       logger.debug("[PWA] beforeinstallprompt event fired");
       
-      // Prevent the mini-infobar from appearing on mobile
-      e.preventDefault();
-      
       // Stash the event so it can be triggered later
       this.deferredPrompt = e as BeforeInstallPromptEvent;