dsh-settings-nav-collapse: A Mobile Navigation Collapse Solution for the DSH Settings Panel

The default layout of the DSH settings panel offers a poor reading experience on narrow screens. The `dsh-settings-nav-collapse` plugin collapses the left navigation bar into a narrow icon rail on narrow screens via a toggle button in the title bar, freeing up width for the main content pane. It supports responsive defaults, state persistence, horizontal panning of the canvas on very narrow screens, and graceful degradation. The plugin uses a style isolation strategy, does not depend on official packages, and is compatible with DSH 0.1.5 and later.