dsh-theme-blackhole: DeepSeek Harness Theme Plugin

`dsh-theme-blackhole` is a theme plugin designed for the DeepSeek Harness (DSH) Web UI, providing a visually striking sci-fi aesthetic. The theme uses WebGL to render a Schwarzschild black hole background through null-geodesic ray tracing, features deep-space glass panels, and incorporates amber accent colors. It supports first-class theme management, bidirectional synchronization with appearance settings, and persistent state, along with performance-friendly fallbacks such as a 30 FPS cap. Installation requires Web service permissions and is only supported in profiles that include a web server. It is open source under the MIT license.