fix(modal): prevent focus from being placed on modal container

[huyenltnguyen]

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Related to freeCodeCamp/freeCodeCamp#66639.

I have not been able to reproduce the issue, so I think this is a race condition.

Likely cause:

• When a modal opens, showFocusRingOnInitialFocus runs via HeadlessUI's afterEnter callback and applies an inline outline style to whatever document.activeElement is at that moment.
• document.activeElement might be the <Dialog> wrapper element itself, so it could receive the blue outline. Since this is a full-viewport fixed element, the blue lines appear at the viewport edges.
• The outline then persists because the element may be removed from the DOM before a blur event fires, so the once: true cleanup listener never runs.

The fix is to guard against applying an outline to body, html, or the dialog container (role="dialog").