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.