dsh-sideband: DeepSeek Harness Asynchronous Context Relay Plugin

dsh-sideband is an MIT-licensed plugin for DeepSeek Harness designed to implement asynchronous LLM summarization context handover. It is suitable for scenarios where the source session is still executing and interrupting the current turn is undesirable. By projecting the visible user and model text within command boundaries, it forms a context package with provenance and delivers it to other Sessions or Agent Team Rooms. Core features include: 1. **Async Processing**: The command immediately returns a Job ID, while the background continues summarizing and delivering; status queries and cancellation are supported. 2. **Independent Summarization**: It uses tool-free, independent LLM calls to process text, excluding sensitive content such as system instructions, reasoning, and tool calls; the `--focus` parameter guides the summarizer only and is not sent to the source model. 3. **Delivery Mode**