Add React Doctor CI

[efazulkarim]

Summary

• Adds .github/workflows/react-doctor.yml using millionco/react-doctor@v2.
• Triggers on pull_request (opened/synchronize/reopened/ready_for_review) and pushes to main.
• Required permissions: contents: read, pull-requests: write, issues: write, statuses: write.
• Concurrency group cancels in-progress runs per PR/ref.

Notes

• No install / build / cache / matrix / token inputs — Action handles all of that with the built-in GITHUB_TOKEN.
• Single new file; no other workflow, script, config, or dependency touched.

[github-actions]

No React Doctor issues found. 🎉

_{Reviewed by React Doctor for commit faf5b9d.}