dsh-skin-center: DeepSeek Harness Skin Center Plugin

`dsh-skin-center` is the official plugin-based theming solution for DeepSeek Harness, designed to address the pain point of manually modifying source code. Through a dual architecture covering both the host and browser, it achieves zero source code modifications, zero screen flickering, and multi-tab synchronization. The plugin includes 35 built-in skins, supports importing and exporting JSON, custom images, and retains the native appearance by default. Installation requires DSH version `0.1.5-rc.2` or later, and on desktop it must be operated from the plugin management interface.