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-troubleshooting.md

@@ -22,7 +22,7 @@ npx vite --version
 
 # Check environment variables
 echo $VITE_PLATFORM
-echo $VITE_PWA_ENABLED
+echo "PWA: automatically enabled for web platforms"
 ```
 
 ### Build System Status
@@ -75,8 +75,8 @@ npm run build:web:dev
 # Clear browser cache
 # DevTools > Application > Storage > Clear site data
 
-# Restart with PWA disabled
-VITE_DISABLE_PWA=true npm run build:web:dev
+# Restart development server
+npm run build:web:dev
 ```
 
 ### Production Build Issues
@@ -414,11 +414,10 @@ ls -la .env*
 
 # Set required variables
 export VITE_PLATFORM=web
-export VITE_PWA_ENABLED=true
 
 # Check in build script
 echo $VITE_PLATFORM
-echo $VITE_PWA_ENABLED
+echo "PWA: automatically enabled for web platforms"
 ```
 
 #### Wrong Environment Loaded