s&box: Real-time external connections with Sandbox.WebSocket — System.Net.WebSockets is sandboxed out

In s&box, WebSocket connections to external services use Sandbox.WebSocket, not System.Net.WebSockets (sandboxed out). Developers need WebSockets for real-time external data (chat, live scores, IoT). The same URL restrictions as Http apply — no IP addresses, HTTPS/WSS only.