v0.3.8 - Reduced motion support

What's changed

• Added prefers-reduced-motion: reduce support for stone placement transitions.
• Added regression coverage so reduced-motion styling stays in CI.
• Updated README, roadmap, accessibility notes, changelog, and package metadata.

Verification

• Node syntax checks passed for src/engine.js and src/main.js.
• Node test suite passed: 22 tests.
• git diff --check passed.
• GitHub Actions CI and Pages deployment passed.