Introducing the DeepSeek Harness (DSH) Workspace File Browser Plugin

`dsh-workspace-files-explorer` provides local file browsing for the DeepSeek Harness (DSH) Web GUI. The plugin displays the file tree of the current session workspace in an overlay panel, supporting drag-to-resize, lazy loading, and code/Markdown preview. It includes security features: it only reads local files, makes no network requests or performs writes, and prevents XSS injection. By adding a button to the title bar, developers can conveniently manage context files and support agent development.