dsh-sess: Session Management and Cleanup Plugin for DeepSeek Harness

`dsh-sess` is a session management plugin for DeepSeek Harness (DSH) that addresses limitations in the original version, specifically the inability to permanently delete sessions and manage archived sessions. The plugin provides both sidebar and Web UI interfaces, supports session lookup, permanent deletion (limited to cold sessions), renaming and deletion of archived sessions, and leverages the official API to ensure compatibility. After installation, it must be enabled in the settings. Currently, only the Web UI is supported, and it does not support unarchiving or deleting active sessions.