The island listened for `ai-for-dummies:language-change` on `document`, but
task 15c dispatches `ai-for-dummies:languagechange` on `window`. Window events
do not reach a document listener, so that path was dead; only the `<html lang>`
MutationObserver was firing.
The focus ring was `3px solid var(--red)` at `outline-offset: 2px`, applied
globally to every button on the page. `responsive.css` uses gold at offset -3px
for exactly these nine groups. Restored, and scoped to them.