use key or code, but not keycode

[todo]

keystack/src/utils/keyboard.js

Lines 21 to 26 in 0c8d251

	/** @todo use key or code, but not keycode */
	const onKeyUp = (event) => {
	if (event.keyCode === 90) {
	// z
	octave = Math.max(--octave, 0)
	} else if (event.keyCode === 88) {

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This issue was generated by todo based on a todo comment in 0c8d251. It's been assigned to @danielgamage because they committed the code.