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/main.web.ts

@@ -2,12 +2,8 @@ import { initializeApp } from "./main.common";
 import { logger } from "./utils/logger";
 
 const platform = process.env.VITE_PLATFORM;
-const pwa_enabled = process.env.VITE_PWA_ENABLED === "true";
 
-// Only import service worker for web builds
-if (pwa_enabled) {
-  import("./registerServiceWorker"); // Web PWA support
-}
+// PWA service worker is automatically registered by VitePWA plugin
 
 const app = initializeApp();