Improve doctor.mjs to check Playwright browser installation

[RajjjAryan]

Summary

npm run doctor should verify that Playwright Chromium is installed.

What to do

1. Open doctor.mjs
2. Add a check that runs npx playwright install --dry-run chromium or checks the browser binary path
3. Print a helpful message if Chromium is not installed: npx playwright install chromium

Acceptance criteria

• Doctor reports Playwright browser status
• Clear fix instruction on failure