Add file sharing and QR code features

- Add file sharing with chunked transfer over data channel
- Display file messages with download button
- Add QR code generation for connection sharing
- Add QR scanner for easy connection joining
- Update UI with file button and scan option
- Add responsive CSS styling for new features

package.json

@@ -11,6 +11,8 @@
   },
   "dependencies": {
     "@xtr-dev/rondevu-client": "^0.0.4",
+    "@zxing/library": "^0.21.3",
+    "qrcode": "^1.5.4",
     "react": "^18.2.0",
     "react-dom": "^18.2.0"
   },