🚀 Enhanced page-navigation plugin with BEM CSS and improved compatibility

✨ Key improvements:
- BEM (Block Element Modifier) CSS methodology implementation
- Updated plugin-utils dependency to v1.1.0
- Professional CHANGELOG.md with release tracking
- Enhanced README.md with BEM documentation and examples
- Modernized package.json metadata and keywords
- BEM-compliant CSS classes (.page-nav, .page-nav__item, .page-nav__link, etc.)
- Configurable activeClass maintains backward compatibility
- Full Nera v4.1.0 compatibility

🎨 BEM CSS Classes:
- .page-nav (main navigation block)
- .page-nav__item (navigation list items)
- .page-nav__link (navigation links)
- .page-nav__link--active (active page link)
- .page-nav--list (list-style navigation)
- .page-nav--pipe-separated (pipe-separated navigation)

🧪 Quality assurance:
- All tests passing (5/5)
- ESLint compliant
- Zero breaking changes
- Template publishing system enhanced