dsh-mpkg-wallpaper: Adding Wallpaper Engine mpkg Backgrounds to dsh Web

`dsh-mpkg-wallpaper` is a DSH Web wallpaper engine plugin developed by XHR666, used to extend the background functionality of the DeepSeek Harness Web interface. This plugin supports parsing Wallpaper Engine's `.mpkg` files within the browser, automatically discovers Steam Workshop directories, and is compatible with video, web page, and image wallpapers. Core features include automatic switching of time-based wallpapers, unified blur and glass appearance theme control, local wallpaper library management, and scheduled rotation. The plugin provides playback controls for video/web page wallpapers and multiple power-saving strategies (such as pausing when unfocused or on battery power), and supports streaming playback of large files exceeding 600MB. Settings can be imported and exported via JSON files for backup and recovery, and it features version checking and one-click update functionality.