dsh-plugin-ui-font-family: Adding Custom Font Support for Web Interfaces

`dsh-plugin-ui-font-family` is a DeepSeek Harness (DSH) plugin designed to support font customization in web interfaces. It supports preset selection, system font usage, and custom font file uploads (TTF, WOFF, etc.), with flexible configuration in the settings menu. Users can install and enable the plugin via the command line. The configuration file can specify a default font or allow manual overrides. Note that uploaded fonts are stored in the `$DSH_HOME/fonts` directory, and the files must be removed manually after the plugin is uninstalled. Fonts in code blocks are unaffected, and remote users can use uploaded fonts but cannot see the list of local system fonts.