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)

Polish visual defects: color cards, spacing, date picker, file attachments, progress, input group, timeline, icon mappings ...

- demo: remove page background layer, add vertical spacing for demo rows
- palette: wrap color swatches in color cards with name/hex labels
- description list: style description-list-term distinctly
- file-upload: shrink attachment cards to 130px, increase gaps, center placeholder text
- forms: add .input-date styling with calendar icon and focus ring
- input-group: seamless action slot button without double borders
- progress: add vertical spacing between consecutive progress bars
- timeline: align marker connector line at left: 23px
- vue: make GnIconButton label optional, add Phosphor icon mappings
- tests: screenshot workflow passing, all 19 e2e tests green

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

Add Popover, Pagination, Timeline and Loader components ...

- Add Popover CSS/browser helper/Vue adapter with click-outside and Escape handling.
- Add Pagination CSS and GnPagination Vue adapter.
- Add Timeline CSS and GnTimeline Vue adapter.
- Add Loader/Spinner CSS/browser helper/Vue adapter with spin/dots/bar variants.
- Wire all four components into the SCSS entry, browser bundle, Vue plugin and exports.
- Add demo partials for popover, pagination, timeline and loader.

E2E and Vue adapter smoke builds pass.