dsh-session-remove: Stop and Permanently Delete a DeepSeek Harness Session in the Sidebar

The `dsh-session-remove` plugin adds “Stop” and “Permanently Delete” actions to the session menu in the DeepSeek Harness sidebar, aiming to improve the session management experience. Implemented via official extension points, it supports stopping running tasks with one click and completely clearing local logs, caches, and workspace records. It is easy to install and has zero dependencies, but deletion is irreversible; after updating, the host module must be restarted for changes to take effect.