Build a typing-speed test as a static web app in this directory: index.html, style.css, app.js, words.js. Random word streams, live WPM and accuracy, a 60-second timed mode and a zen mode, per-key error highlighting, results screen with WPM history chart on a canvas, high scores in localStorage, dark theme, and tests.html + tests.js exercising the WPM/accuracy math. Run the tests headless with node and fix what fails.