dsh-session-delete: Add a Delete Button to the Session Header

The DeepSeek Harness plugin `dsh-session-delete` adds a red trash can button to the right side of the session header, aiming to address the issue of the official archive entry being concealed. Through a hover-revealed interaction, the plugin provides one-click session deletion and invokes the official API to enable persistent archiving. It supports both local and npm installation, has no side effects, and is easy to uninstall, offering users a standardized session cleanup experience.