v0.3.1 - High contrast display toggle

What's changed

• Added a local high-contrast display toggle for the browser game.
• Made the board edge follow the high-contrast theme instead of keeping the default wood-tone border.
• Updated contributor suggestions after completed player-name and computer-mode work.

Verification

• Node syntax checks passed for src/engine.js and src/main.js.
• Node test suite passed: 14 tests.
• GitHub Actions CI and Pages deployment passed.