feat: implement secure browser notifications system

- Added SecureNotificationManager with cross-browser support (Chrome, Firefox, Safari, Edge)
- Integrated WebRTC message notifications with tab visibility detection
- Implemented XSS protection, URL validation, and rate limiting
- Notifications shown only when chat tab is inactive
- Enforced HTTPS and user gesture requirements

sw.js

@@ -27,11 +27,7 @@ const STATIC_ASSETS = [
     '/src/pwa/pwa-manager.js',
     '/src/pwa/install-prompt.js',
     '/src/scripts/pwa-register.js',
-    '/src/scripts/pwa-offline-test.js',
-    
-    // Bluetooth key transfer (PWA feature)
-    '/src/transfer/BluetoothKeyTransfer.js',
-    '/src/components/ui/BluetoothKeyTransfer.jsx'
+    '/src/scripts/pwa-offline-test.js'
 ];
 
 // Sensitive files that should never be cached