dsh-session-mgr: DeepSeek Harness Web Session Management Plugin

The DeepSeek Harness plugin `dsh-session-mgr` is designed to address the inconvenience of session management in the web interface. It supports moving, archiving, restoring, backing up, and deleting sessions, as well as cross-workspace operations. Users can generate compressed packages containing logs and attachments, then seamlessly restore sessions on another machine via the import function. The plugin provides a multilingual interface and batch operations, and supports managing sessions directly through the settings page. Installation requires the command line and enabling the plugin in the configuration. Operations on active sessions must be performed after unloading them first, and deleted sessions cannot be recovered.