dsh-open-workspace: Add a Workspace Folder Entry Point to DeepSeek Harness Web

The dsh-open-workspace plugin injects two entry points (a sidebar menu and a title bar button) to seamlessly integrate file system operations into the DeepSeek Harness Web GUI. It supports opening the workspace root directory by session ID or workspace path, preferring to launch the system file manager. Installation options include local and remote scripts. It is compatible with DSH 0.1.2 and resolves the issue of a broken workflow between the web interface and local file system operations.