dsh-workspace-tree: DeepSeek Harness Virtual Session Folder Management Plugin

`dsh-workspace-tree` is a plugin for DeepSeek Harness (DSH) designed to solve the issue of scattered sessions and physical directories caused by long-term use. By introducing a virtual session folder mechanism, it enables session grouping and management with zero filesystem pollution. Core features include multi-workspace stability, folder-scoped session creation, active task banners, precise session movement, and an in-app visual directory browser. It also supports session pinning, inline renaming, and a 0ms responsive engine, significantly improving session management efficiency in multi-workspace setups after installation.