Closes#1741. Two small a11y polishes on the native `<details>` /
`<summary>` primitive:
- Add a token-backed focus-visible ring on `<summary>`. Previously
inherited only the browser default outline, which was thin and
inconsistent across engines. Match the new pattern from #1738:
`outline-2 outline-offset-2 outline-gray-900` plus
`theme-dark:outline-white` so the ring lands on the page chrome
outside the disclosure regardless of mode. (WCAG 2.4.7.)
- Gate the chevron rotation behind `motion-safe:transition-transform`
+ `motion-safe:duration-150`. The chevron now slides between
closed/open states for users who haven't opted out of motion, and
snap-rotates instantly under `prefers-reduced-motion: reduce`.
(WCAG 2.3.3, AAA.)
While here: drop the no-op `group-open:transform` class. Tailwind
v4 applies `rotate-90` / `rotate-180` directly without needing the
explicit `transform` utility — it was a v3 holdover.
