Add Overlays browser helper ...

- Implement Overlays helper for dropdown and tooltip toggle management
- Avoid conflict with existing popover.js by not handling data-popover-toggle
- Add CSS support for .dropdown.is-open and .tooltip.is-open
- Add overlays demo partial
- All 17 e2e tests pass, no console errors

Co-Authored-By: Claude <noreply@anthropic.com>