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/libs/fontawesome.ts

@@ -36,6 +36,7 @@ import {
   faComment,
   faCopy,
   faDollar,
+  faDownload,
   faEllipsis,
   faEllipsisVertical,
   faEnvelopeOpenText,
@@ -121,6 +122,7 @@ library.add(
   faComment,
   faCopy,
   faDollar,
+  faDownload,
   faEllipsis,
   faEllipsisVertical,
   faEnvelopeOpenText,