Add Vue components and demo mounts for divider, step, chips, avatar, choices, select, textarea, pagination, loader ...

- Create GnDivider and GnStep Vue components.
- Export GnStep and GnDivider via plugin and index.
- Update GnSteps to render check icon for complete steps.
- Add Vue demo mounts to divider, stepper, select-textarea, pagination, loader, chips, avatar, choices partials.
- Convert chips and avatar partials to demo-section for screenshot capture.
- Expand screenshot section list.
- All 19 e2e tests green.

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