feat: add remaining reference Vue components, card variants, toolbar/repeater/activity-log/usage-meter styles and demo mounts ...

- Add GnHorizontalCard, GnUserCard, GnMetricCard, GnStatusCard, GnLoginCard,
  GnIdentity, GnActivityLog, GnToolbar, GnRouterTabs, GnRepeater, GnUsageMeter
- Extend GnTabs to support reference items API while keeping child mode
- Add card subcomponent styles: status, metric, horizontal, login, user
- Add toolbar, repeater, identity, activity-log, usage-meter styles
- Add typography token variables used by reference-compatible components
- Add Vue demo mounts for cards, data-patterns, progress, tabs, navigation-shell
- Fix GnAvatar online status class and navigation-shell footer slot
- Update screenshot config to cover skeleton and navigation-shell

Verified: npm run build, npm run test:e2e (19 passed), npm run screenshots,
npm run test:vue-adapter, figma-match (7 passed)

Add GnAvatarStack, GnChipGroup, GnCombobox and GnSearchField Vue components ...

- Mirror reference gnexus-ui-kit API for avatar stack, chip group, combobox and search field.

- Add supporting styles for .avatar-stack, .avatar-xs and .chip-group.

- Add Vue demo mounts to avatar, chips, advanced-select and inputs partials.

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

Add Tabs, Avatar, Chip, and Progress components ...

- Implement pill/compact/vertical tabs with browser helper and Vue adapters
  (GnTabs, GnTab, GnTabPanel) plus keyboard navigation.
- Add Avatar styles and GnAvatar with initials/image/icon and status dot.
- Add Chip styles and GnChip removable/selectable chip.
- Add Progress styles, browser helper, and GnProgress linear/step.
- Wire new components into kit.scss, Vue plugin, Vue entry, and browser bundle.
- Add demo partials and update docs/component-coverage.md + PROJECT_NOTES.md.
- All builds and smoke tests pass.