dsh-feishu-gateway: Connect DeepSeek Harness agent to Feishu

`@kriskwok/dsh-feishu-gateway` is a plugin designed to route Feishu messages to a DeepSeek Harness (DSH) agent, enabling users to interact with a local DSH via Feishu private or group chats without requiring public webhooks. By leveraging Feishu long connections, it supports persistent session management; Feishu conversations or group topics can be mapped to independent DSH sessions, and new sessions can be initiated via `/new` or natural language instructions. Functionally, it offers Markdown rich text replies, native Typing status indicators, streaming progress cards for long tasks, and button-based approval and Q&A interactions. Web-specific interaction components automatically fallback to readable prompts on the Feishu side. DSH must be configured prior to use.