Add vitepress-md-react-preview plugin for interactive UI component preview

[IzumiSy]

Summary

Integrate md-react-preview (mrp) into docs.tailor.tech to provide live interactive previews for AppShell component documentation pages.

Background

AppShell's component documentation is authored as Markdown in the app-shell repository and synced to this repository (docs.tailor.tech) for rendering with VitePress.

In tailor-platform/app-shell#250, mrp was integrated on the AppShell side to enable local component preview via pnpm docs:preview. This PR is the counterpart on the docs.tailor.tech side — it adds the VitePress plugin so that the same preview blocks render as live interactive components in production.

What is mrp?

md-react-preview (mrp) is a toolchain that enables Storybook-like live React component previews directly inside Markdown documentation. It provides both a Vite plugin and a VitePress plugin sharing the same rendering core:

• AppShell repository: Authors run pnpm docs:preview to preview documentation locally (via mrp dev)
• docs.tailor.tech: The same previews are rendered in production via the VitePress plugin (@izumisy/vitepress-plugin-react-preview)

This allows documentation authors to write ```tsx preview code blocks in Markdown and get identical interactive results both locally and in production.

Changes

• Added @izumisy/vitepress-plugin-react-preview (^0.3.0), @tailor-platform/app-shell, react, and react-dom as dev dependencies
• Configured mrp in .vitepress/config.mts — registers the Vite plugin and markdown-it plugin with AppShell's CSS (@tailor-platform/app-shell/styles)
• Registered PreviewBlock Vue component globally in .vitepress/theme/index.ts
• Updated docs/app-shell/components/button.md to use the new preview fence syntax (export default (...) with fragment wrappers)

How to test

pnpm install
pnpm dev

Open http://localhost:5173/app-shell/components/button and verify that the "Basic Usage" section renders live interactive Button components.