dsh-mobile-nav: Ultra-Lightweight Mobile UI Plugin for DeepSeek Harness

`dsh-mobile-nav` is an ultra-lightweight mobile-optimization plugin designed specifically for the DeepSeek Harness Web UI. It is implemented as a single file, does not modify the source code, and only applies to viewports ≤640px. Core features include collapsing the sidebar into a drawer to save space, simplifying the header and message action rows, displaying a statistics panel when tapping the input box icon, and adding link preview support. The plugin relies entirely on official CSS Modules semantic class names and supports customizing styles and hidden items by modifying `lib/client.js`, with no build step required—just refresh the browser to apply changes.