Motivation

• Provide a mobile-first visual preset to make the component library feel more native on touch devices.
• Let the demo showcase and persist the preset so designers can preview the mobile look interactively.
• Ship the theme file as part of the package so consumers can opt into the preset without hacking the source.

Description

• Add src/themes/mobile-native.css which defines data-theme="mobile-native" tokens and component deltas for a mobile-native look (surfaces, buttons, inputs, segmented controls, shadows, and motion).
• Expose the new preset via the package exports and update the build script to copy src/themes/*.css into dist/themes/ so ./themes/mobile-native.css is available to consumers.
• Update the demo: import the theme in demo/src/style.css and extend demo/src/theme-customizer.tsx with DemoTheme state, applyDemoTheme, UI buttons to toggle the preset, and persistence to localStorage under pui-demo-theme.
• Document the preset in docs/pages/theming.md with usage notes and the data-theme example.

Testing

• Ran the test suite with pnpm test (Vitest) and the tests succeeded.

Codex Task