dsh-logo-silhouette: Add a non-blocking whale background watermark to DSH Web GUI.

dsh-logo-silhouette is a Web GUI plugin for DeepSeek Harness (dsh) developed by kami-mura. It utilizes the plugin mechanism to set the DeepSeek whale logo silhouette as a full-screen background watermark, requiring no modification of the frontend source code. The plugin is purely visual with zero host logic: the background layer is set to `pointer-events: none` to prevent blocking interactions, the whale is fixed to the bottom-left corner, and it automatically adapts to light and dark themes with a 300ms smooth transition. In night mode, it features a fade-in effect, anti-glare, and narrow-screen adaptation. Installation requires only...