Add Jest regression suite + refresh README (2025) + safe npm publish config

[Winner95]

Summary

This PR modernizes the repo for a smoother “vNext” workflow: adds a proper regression test harness with real-world TS fixtures, refreshes the README with a current step-by-step guide + compatibility notes, and prevents accidental latest publishes.

---

What changed

✅ Testing

• Added Jest setup (jest.config.cjs) + scripts: test, test:watch, test:coverage.
• Introduced a growing set of fixtures covering common + tricky TS/React prop patterns (polymorphic props, generics/defaults, exported types/interfaces, etc.).
• Captured a couple of known limitations as explicit “expected to throw” tests (so regressions are visible and behavior is documented).

📚 Docs

• Rewrote/expanded README for 2025:
  • Clear “Why this exists” explanation
  • Step-by-step quick start (copy/paste docgen script)
  • Compatibility matrix + roadmap note for react-docgen v6
  • “Covered vs not covered” section
  • Disclaimer + support/responsibility notes
  • Links to live sandboxes (with/without handler)

🧯 Release safety

• Added .npmrc to default publishes to a non-latest tag (safer vNext iteration / pre-release flow).

---

Why

This handler is small and purpose-built, but TypeScript + React prop typing patterns are not. The new fixture-based test suite makes it much easier to:

• validate behavior across real patterns,
• document current gaps,
• and confidently iterate toward the planned 2.x / react-docgen 6.x support.

---

How to test

yarn test
yarn test:watch
yarn test:coverage