feat(Carousel): fix contrast issue in carousel bullets

[aweell]

Context

Carousel bullet indicators lack sufficient contrast between selected and unselected states, failing accessibility standards.

Upstream design issue: Telefonica/mistica-design#2388
Jira: DSNCORE-2256

Specs

https://www.figma.com/design/hxJvuIQQ1xf50xIOQFUZbQ/%F0%9F%94%B8-Carousel-Specs?m=auto&node-id=483-4281&t=KoGiySn1u5pTBi06-1

Tasks

• Update bullet indicator tokens/styles to achieve sufficient contrast between selected and unselected states
• Introduce a plain-text page counter as an alternative to bullet-based navigation (if specified in design)
• Update stories and snapshots accordingly
• Verify contrast compliance across all skins