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.