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.

docs/build-systems-overview.md

@@ -38,7 +38,7 @@ All build scripts follow a consistent pattern:
 ```bash
 # Set platform-specific environment variables
 VITE_PLATFORM=<platform>
-VITE_PWA_ENABLED=<true/false>
+PWA: automatically enabled for web platforms
 VITE_GIT_HASH=<git-commit-hash>
 ```
 
@@ -212,8 +212,7 @@ All build systems use consistent environment variable patterns:
 VITE_PLATFORM=web|capacitor|electron
 
 # PWA configuration
-VITE_PWA_ENABLED=true|false
-VITE_DISABLE_PWA=true|false
+PWA: automatically enabled for web platforms
 
 # Build information
 VITE_GIT_HASH=<git-commit-hash>
@@ -396,7 +395,7 @@ xcrun devicectl list devices
 ```bash
 # Verify environment variables
 echo $VITE_PLATFORM
-echo $VITE_PWA_ENABLED
+echo "PWA: automatically enabled for web platforms"
 
 # Check environment files
 ls -la .env*