feat: add keyboard navigation support for DisplayCarousel via node selection

## Summary

DisplayCarousel keyboard navigation currently only responds to `focusin`/`focusout` on its own containers. When used inside vueNodes, node selection alone should be enough to expose gallery controls and drive left/right navigation without requiring inner focus.

## Context

Identified during review of #9712. Scoped out as a separate enhancement.

## Acceptance Criteria

- Node selection activates gallery keyboard controls
- Left/right arrow keys navigate images when node is selected
- Works without requiring explicit focus on the carousel container

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-9776-feat-add-keyboard-navigation-support-for-DisplayCarousel-via-node-selection-3216d73d365081c198f2f5e6072437a5) by [Unito](https://www.unito.io)