Add CoWorker Protocol — P2P agent collaboration over XMTP

[ZiwayZhao]

Adds CoWorker Protocol to the list under Multi-Agent Communication.

CoWorker is an open-source Python protocol for P2P agent collaboration:

• Schema-based skill invocation (peers see contracts, not code)
• E2E encrypted via XMTP production network
• Revocable trust tiers with auto-downgrade
• Async delegation — peers don't need to be online simultaneously
• Zero dependencies, MIT licensed

GitHub: https://github.com/ZiwayZhao/agent-coworker
PyPI: https://pypi.org/project/agent-coworker/