Add GnAvatarStack, GnChipGroup, GnCombobox and GnSearchField Vue components ...

- Mirror reference gnexus-ui-kit API for avatar stack, chip group, combobox and search field.

- Add supporting styles for .avatar-stack, .avatar-xs and .chip-group.

- Add Vue demo mounts to avatar, chips, advanced-select and inputs partials.

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