dsh-wecom-plugin: Bidirectional Connection Between WeCom and DeepSeek Harness

`dsh-wecom-plugin` is a proof-of-concept plugin that enables bidirectional connectivity between a WeCom Intelligent Bot and DeepSeek Harness (DSH). By implementing the official protocol, it supports long-lived connections, streaming responses, and session isolation, allowing DSH agents to be invoked directly within WeCom. The plugin supports local mock testing and end-to-end demonstrations, with complete handling of protocol details and permission authorization. Installation requires using the `file:` prefix and configuring WeCom credentials.