dsh-dracula-theme: Apply the classic Dracula dark theme to DeepSeek Harness

# Introduction When using the Web GUI of DeepSeek Harness (DSH), the visual appearance follows the client's color scheme. If you want to switch to a pleasing dark theme, the conventional method is to fork the client and manually edit the CSS. This is tedious and requires rebasing every time you upgrade. DSH's philosophy is "Everything is a plugin." The client has a built-in theme runtime, allowing color schemes to be registered as plugins without modifying the client source code. The `dsh-dracula-theme` introduced below is precisely such a theme plugin: it brings the classic Dracula dark color scheme to DSH. # What is this `dsh-dracula-theme` is maintained by ossFrankFrank and is released under the MIT License. It is based on the official Dracula...