DeepSeek Harness SideChat Plugin

The DeepSeek Harness SideChat plugin adopts a modular plugin architecture to provide DSH with persistent, standalone clarification sessions. Users can create a SideChat via the `/side` command, with support for multiple Seed strategies and read-only or inherited permission modes. Built on DSH’s native Session mechanism, the plugin supports session archiving, Fold generation, and referencing parent sessions, while offering comprehensive Token tracking and immutable provenance. The plugin has only been verified against DSH 0.1.2-alpha.1. Uninstalling it does not affect previously created sessions, making it suitable for context isolation and independent verification scenarios in long-chain development.