Document Entra oauth2-proxy deployment

[iamlukethedev]

Summary

• Add a deployment guide for running Claw3D behind Microsoft Entra ID, oauth2-proxy, nginx, and TLS.
• Cover Entra app registration, oauth2-proxy config, nginx reverse proxy and WebSocket upgrade config, Claw3D env vars, webhook signing, health checks, and troubleshooting.
• Link the guide from README common setups/documentation and Security deployment notes.

Testing

• git diff --check
• Manual documentation review.