docs: host docs on Vercel at rne.appandflow.com

[charlesvinette]

Summary

Moves the docs site from GitHub Pages (appandflow.github.io/react-native-ease) to Vercel at https://rne.appandflow.com.

• docs/docusaurus.config.ts: url → https://rne.appandflow.com, baseUrl → /
• vercel.json (new): installs only the docs workspace (yarn workspaces focus docs, so we skip the example app's React Native deps) and publishes docs/build. An ignoreCommand skips Vercel builds for commits that don't touch docs/ or vercel.json.
• Removes the GitHub Pages publish workflow (docs-deploy.yml) and docs/static/.nojekyll. docs-check.yml still builds the docs on PRs.
• docs/README.md: updated the deployment note.

Vercel setup (already done): the react-native-ease project exists in the appandflow team and rne.appandflow.com is attached to it. DNS and SSL are handled automatically because the zone is on Vercel.

The Vercel project is linked to this repo with main as the production branch. Merging this PR deploys to production, and PRs get preview deployments.

Test Plan

• Ran yarn workspaces focus docs && yarn workspace docs build locally. The build succeeds and all asset/link paths are rooted at /.
• Deployed this branch with the Vercel CLI. As the project's first deployment, Vercel promoted it to production, so it's live now. Checked on https://rne.appandflow.com:
  • /, /docs/, /docs/usage and /docs/api-reference return 200
  • /img/app-icon.png returns 200
  • unknown paths return the 404 page

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