Move 13 shadcn UI components, cn() utility, and theme CSS variables
to packages/ui for cross-platform reuse. Add @source directives for
Tailwind v4 content scanning.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Shared UI package for web, electron, and mobile. Uses subpath exports
following the official shadcn monorepo template pattern.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>