dsh-ui-wallpaper: DeepSeek Harness Wallpaper Plugin

`dsh-ui-wallpaper` is a plugin designed for the DeepSeek Harness Web GUI, intended to emulate Wallpaper Engine’s mechanism, allowing users to set local images, GIFs, or videos as dynamic backgrounds and adjust interface transparency. The plugin achieves this effect through a three-layer overlay, supports background brightness adjustment (20%–200%), and provides GIF/video playback speed control (0.1x–5x). It also supports one-click imports of Wallpaper Engine wallpapers (requires ffmpeg). When installing, pay attention to pnpm version compatibility and system permissions.