- 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>

- Implement Table styles + browser helper + GnTable/GnTableRow/GnTableHeader
  with sortable/selectable variants.
- Implement List styles + browser helper + GnList/GnListItem.
- Implement Skeleton placeholders + browser helper + GnSkeleton.
- Implement Tooltip styles + browser helper + GnTooltip.
- Implement Dropdown menu styles + browser helper + GnDropdown/GnDropdownItem.
- Implement NavigationShell layout + browser helper + GnNavigationShell/GnNavigationItem.
- Wire all new components into kit.scss, Vue plugin, Vue entry, and browser bundle.
- Add demo partials for every new component.
- Update docs/component-coverage.md and PROJECT_NOTES.md.
- Builds and tests pass.