feat(mint): add reduced-motion accessibility audit

[nujovich]

Card: https://github.com/nujovich/mint-radar/issues/27

What: Adds a reduced-motion accessibility audit to Mint's CSS lint rules. Milestone 1 added the MotionAccessibilityAudit type system and a lintMotionAccessibility() scanner that detects animation and transition declarations sitting outside a @media (prefers-reduced-motion: reduce) wrapper. Milestone 2 extends the parser to also flag transform declarations and to skip @keyframes internals so keyframe transform steps are not reported as unwrapped motion.

Why: stylelint has had an open request for a prefers-reduced-motion rule since 2022 with no core implementation. Users who opt into reduced motion should not receive full-strength animation, transition, or transform effects. Mint already performs semantic CSS auditing but had no motion-safety check, so this closes that a11y gap.

Milestones

• Milestone 1 — Add MotionAccessibilityAudit type system detecting animation/transition declarations without a @media (prefers-reduced-motion) wrapper
• Milestone 2 — Implement parser identifying animation properties (animation, transition, transform) and verifying reduced-motion wrapping
• Milestone 3 — Add report with count of animations not respecting user motion preference and wrap suggestion
• Milestone 4 — Add tests with the stylelint prefers-reduced-motion rule dataset

Milestone 2 detail

Extended lintMotionAccessibility() in lib/css-lint-rules.mjs:

• Added transform to the MOTION_PROPERTIES set so unwrapped transform declarations are flagged alongside animation / transition and their longhands.
• Added a @keyframes stack (mirroring the existing reduced-motion stack) so declarations inside @keyframes blocks — whose transform steps define the animation itself — are skipped, and only the element's animation reference is reported. Handles vendor-prefixed forms such as @-webkit-keyframes.
• Updated the MotionAccessibilityIssue.property doc comment in lib/types.ts to include transform.
• Added a test verifying an unwrapped transform is flagged while keyframe internals remain ignored.

Tests

All 774 tests passing:

npm test

How to test:

npm test
# or scoped: npx vitest run lib/__tests__/css-lint-rules.test.mjs