feat: add all integration examples and Pages preview

[VdustR]

TL;DR

Adds a reviewable first version of @vp-tw/react-live with one package, explicit subpath exports, every supported integration under examples/, and a GitHub Pages deployment workflow.

Included

• Vite, Rollup, Webpack, and Rolldown adapters
• Default and custom React renderers
• Docusaurus integration with SSR/client parity
• Astro Starlight integration
• One Pages index for all seven production-built demos
• React 18 and 19 fixtures
• Node 22 and 24 CI coverage

Verification

• corepack pnpm peers check
• corepack pnpm typecheck
• corepack pnpm test (10 tests)
• corepack pnpm build:pages
• Browser render and click interaction for all seven demos under /react-live/
• Packed tarball contents, every ESM entry, and the Docusaurus CommonJS entry
• git diff --check

Known review items

• Docusaurus currently brings in image-size advisories with no patched release listed by the registry audit. It is confined to the private documentation build fixture.
• The editable runtime currently bundles Babel standalone, so example bundles are intentionally large; lazy loading is a follow-up performance decision.
• No npm publication, legacy repository archival, or redirect is included.

Closes part of #1.