dsh-admin: DeepSeek Harness Web GUI Administration Plugin

`dsh-admin` is a Web GUI management plugin for DeepSeek Harness, designed to address service restart and version update issues. It provides a manual restart feature that stops, cleans up instances, and starts the service via a `systemd` script. The plugin supports automatic version checks (once every 6 hours) and displays a version status indicator. When a new version is detected, it can be installed automatically through a one-click update button. The interface can be embedded in the Web header tool slot or settings page and supports updates via API calls. It is suited for Linux + systemd environments and simplifies the operations and maintenance workflow for agent development.