dsh-provider-copilot: Integrating GitHub Copilot with DeepSeek Harness

DeepSeek Harness (DSH) provides a plugin-based architecture for extending model providers. The `dsh-provider-copilot` plugin bridges a GitHub Copilot subscription to DSH, allowing it to be used within a unified interface. It supports streaming chat, reasoning stream pass-through, management commands, and observability, and automatically discovers Copilot models after installation. Users should be aware of limitations such as the risks associated with non-public APIs, User-Agent requirements, and lack of tool-call support.