Add browser-based format tests covering major parsers
- Create format test runner HTML page for browser testing
- Add browser-format.test.js with tests for multiple parsers
- Test JavaScript, TypeScript, JSON, CSS, Markdown, and HTML
- Validate idempotent formatting in real browser environment
- All format tests pass in Chrome via Puppeteer
Co-authored-by: fisker <172584+fisker@users.noreply.github.com>
