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 Divider, Accordion, Stepper and FileAttachment components ...

- Implement CSS for divider, accordion, stepper and file-upload/attachment.
- Add browser Accordion helper and expose it on window.VMKUIKit.
- Add Vue adapters: GnAccordion, GnSteps, GnFileUpload, GnFileAttachment.
- Add demo partials and figma match pages for divider and attached-file.
- Fix Figma comparison flattening for transparent baselines (e.g. breadcrumbs, attached-file).
- Add vertical spacing to the demo index page to separate sections.

All Figma visual tests and the Vue adapter smoke build pass.