feat: add prefers-reduced-motion support for animations

[Ragnar-no-sleep]

Context

public/index.html uses several CSS animations (orb floating, gradient shifts, spin animations). These run unconditionally — users who prefer reduced motion (vestibular disorders, motion sensitivity) get no option to disable them.

Problem

/* Current — no motion preference check */
.orb { animation: drift1 20s ease-in-out infinite; }
.loading-spinner { animation: spin 1s linear infinite; }

Proposed fix

/* Respect user OS preference */
@media (prefers-reduced-motion: reduce) {
  .orb { animation: none; }
  .loading-spinner { animation: none; }
  .animated-gradient { animation: none; }
  /* Keep functional transitions (e.g. tab switching) */
  .tab-content { transition: none; }
}

Why now

• Accessibility requirement (WCAG 2.1 criterion 2.3.3)
• Governance platforms have broad user bases — motion sensitivity is common
• ASDF-Web design system already includes this pattern in all 5 tool pages

Effort

XS — add one @media block at the bottom of inline CSS

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From ASDF-Web accessibility audit — 2026-02-25