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.