dsh-session-plus: Session Archiving and Branching Plugin for DeepSeek Harness

`dsh-session-plus` is a DeepSeek Harness plugin designed to complement the limitations of the official archiving feature. It provides session archiving, restoration, deletion, and conversation branching through a sidebar directory. The plugin supports idle waiting to prevent log corruption during archiving and disables archiving while tools are being invoked. It does not modify core files and relies on public APIs, ensuring compatibility and security.