DeepSeek Harness Custom Context Menu Plugin

`dsh-custom-context-menu` is a custom right-click menu plugin for the DeepSeek Harness Web UI. It globally intercepts the `contextmenu` event and provides a zero-dependency extension framework. The plugin allows developers to register various menu items—such as regular items, separators, and destructive actions—via its API, and includes a built-in feature for opening workspace folders in a file explorer. It supports keyboard navigation, passes through the native menu when no matching items exist, and is fully compatible with Windows, macOS, and Linux, making it easy for developers to deeply integrate system tools.