dsh-ui-appearance: DeepSeek Harness Appearance Customization Plugin

dsh-ui-appearance is the appearance customization plugin for DeepSeek Harness, supporting both WebUI and DSH Desktop. Key features include: customizing six theme colors (primary, background, panel, input box, text, border) with color picker and HEX input support; wallpaper/video backgrounds (supporting JPG/PNG/WebP/GIF/MP4/WebM, stored in IndexedDB at original quality, with a 200MB limit for images and 50MB for videos); frosted glass and semi-transparent effects (adjusting opacity and blur intensity for panels, input boxes, and code blocks); and background ambiance adjustments (opacity, blur, mask). It includes six preset color schemes and supports exporting/importing color schemes via JSON for sharing. All changes are previewed in real-time and automatically persisted to localSt