dsh-unknown-theme: Port the DeepSeek official website visuals to DeepSeek Harness

dsh-unknown-theme is a community plugin maintained by ycqaq233 under the MIT license, designed to optimize the visual effects of the DeepSeek Harness (DSH) Web workspace to closely resemble the official look of deepseek.com. Not an official component, this plugin is implemented using pure CSS/DOM/Canvas, has zero dependencies, requires no build process, and supports adaptive light/dark dual themes. Its core features include porting the official site's WebGL fluid background, mouse-interactive grid (HeroGrid), particle fish-shaped logo animation, title spotlight effects, and UI component styles featuring a frosted glass texture. Installation is recommended by executing `dsh plugin --profile web add ycqaq233/dsh` via the git repository.