dsh-wallpaper-skin: Change the wallpaper for dsh Web

dsh-wallpaper-skin is a persistent plugin for DeepSeek Harness (dsh) developed by ddbj-hub, designed to provide a custom wallpaper background for the Web interface. This plugin supports static images (jpg/png/webp) and silent looped videos (mp4/webm), replacing the application background with user-specified local files and employing a semi-transparent panel design to minimize interface occlusion. Implemented based on the Cordis plugin architecture and Webserver routing, it remains effective after a single installation and is compatible with both Dark and Light modes. Users can install it via the `dsh plugin` command, manual configuration of `cordis.patch.yml`, or local file dependencies. The configuration path requires filling in the absolute path of the wallpaper file in the settings page and modifying it.