Add an applied modal accessibility debugging lab to Accessibility tooling

### MDN URL

https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Accessibility/Tooling

### What specific section or headline is this issue about?

Testing accessibility during development

### What information was incorrect, unhelpful, or incomplete?

The page explains automated audit tools and assistive technologies, but it does not include an applied scenario showing why an interface can look correct and pass basic automated checks while keyboard and screen-reader behavior still fails. A practical manual-testing example would complement the existing tooling guidance.

### What did you expect to see?

I expected an optional hands-on learning resource that lets learners inspect a realistic modal, identify missing dialog naming, focus escape, background isolation, and focus-restoration problems, and connect those failures to manual testing.

### Do you have any supporting links, references, or citations?

https://frontendatlas.com/incidents/modal-screen-reader-failure

### Do you have anything more you want to share?

Disclosure: I am the founder and maintainer of FrontendAtlas and created the suggested resource. The linked lab is public and requires no account; separate parts of the site contain optional premium exercises.

I am opening an issue first and will only propose a content change if maintainers consider the external resource appropriate.

### MDN metadata

_No response_

Start with the “Testing accessibility during development” section at the MDN Accessibility tooling page and review the proposed modal lab at the linked FrontendAtlas resource. Confirm that the resource fits MDN guidance and link policy, then add an optional hands-on reference covering the listed manual-testing failures if maintainers approve it.

Written by the indexing model from the issue text.