media modals: remove tabindex from images and tab trap

[jivey]

https://openstax.atlassian.net/browse/CORE-1590
https://openstax.atlassian.net/browse/CORE-1546

[Copilot]

Pull request overview

Improves media modal keyboard accessibility by removing an unnecessary tab stop on modal images and introducing a focus trap within the modal dialog.

Changes:

• Removed tabIndex={0} from the modal-rendered <img> so images are no longer in the tab order.
• Added useTrapTabNavigation to the media modal wrapper to trap Tab navigation within the dialog while open.
• Updated related tests to stop relying on img[tabindex="0"] selectors and to reflect the new default tabIndex behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/app/content/components/Page/mediaModalManager.tsx	Stops adding tabIndex to the modal image content.
src/app/content/components/Page/mediaModalManager.spec.tsx	Updates expectation for the modal image’s tabIndex to reflect default behavior without an explicit attribute.
src/app/content/components/Page/MediaModal.tsx	Adds a ref + useTrapTabNavigation to trap keyboard tabbing inside the modal dialog.
src/app/content/components/Page/MediaModal.spec.tsx	Minor formatting-only change.
src/app/content/components/Page.spec.tsx	Updates DOM queries in tests to locate the modal image via the dialog container rather than tabindex.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

useTrapTabNavigation(wrapperRef, isOpen) introduces new keyboard-navigation behavior for the media modal, but the existing MediaModal.spec.tsx coverage doesn’t exercise tab trapping (e.g., Tab/Shift+Tab wrapping and ensuring focus can’t leave the dialog). Consider adding a DOM-based test (similar to mediaModalManager.spec.tsx) that opens the modal, focuses the close button, dispatches Tab/Shift+Tab keydown events, and asserts focus remains within the modal elements.

[RoyEJohnson]

This is a good idea, too.

[RoyEJohnson]

I adjusted the failing test. I was a little surprised it came out -1 rather than null or something, but I'm guessing that's an implicit default for image?
In any case, the behavior is as expected.

[RoyEJohnson]

I have to concede that Copilot makes a good point about testing the tab-trapping.