dsh-manage-sessions: DSH Session Management Plugin

The dsh-manage-sessions plugin provides native UI enhancements for the DeepSeek Harness (DSH) sidebar, addressing session management pain points. Core features include session grouping, batch archive/restore/delete, a two-stage force stop for stuck sessions (auto-resume or remain offline), workspace path copying, and session detail viewing. The plugin supports zero-configuration installation, but requires a compatible DSH version, and the permanent deletion feature depends on a specific patch. It leaves no residue after uninstallation and is well suited for developers who frequently manage multiple sessions.