dsh-open-folder: DeepSeek Harness Session Header Folder Navigation Plugin

`dsh-open-folder` is a Web UI plugin for DeepSeek Harness (DSH) designed to provide a "one-click Open Workspace" feature. The plugin adds an "Open Workspace" button to the session header toolbar, allowing developers to directly invoke the Host's `workspaces.openPath()` method to open the `cwd` directory of the current Session, quickly bridging the Web UI and the local file system. Installation is simple and requires only running the specified command in the terminal, making it suitable for developers who frequently need to locate working directories during development and debugging.