test(web): reduced motion disables all motion

Also turns off the fold height transition, which the universal selector does not reach (::details-content).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ui/src/tokens.css

@@ -97,4 +97,6 @@ code, pre { font-family: var(--mono); }
 @media (prefers-reduced-motion: reduce) {
   *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
   ::view-transition-group(*), ::view-transition-old(*), ::view-transition-new(*) { animation: none !important; }
+  /* separate rule: browsers without ::details-content drop only this one */
+  *::details-content { transition: none !important; }
 }

packages/ui/test/motion-css.test.ts

@@ -88,6 +88,8 @@ test("prefers-reduced-motion turns off every animation, transition and view tran
   expect(block).toMatch(/::view-transition-group\(\*\)/);
   expect(block).toMatch(/::view-transition-old\(\*\)/);
   expect(block).toMatch(/::view-transition-new\(\*\)/);
+  // `*` does not reach ::details-content (fold heights), so it has its own rule.
+  expect(block).toMatch(/\*::details-content\s*\{\s*transition:\s*none !important/);
 });
 
 test("view transitions never take pointer input and keep the header and sidebar still", () => {