JavaScript Piano Keyboard

Not sure if anyone has suggested this topic before but here it is in case it hasn't. The piano should use equal temperament tuning ([this](https://en.wikipedia.org/wiki/Equal_temperament#Twelve-tone_equal_temperament)) where each note is multiplied by the twelfth root of 2 to get a half step up. Also an A is at 440 hertz.

The issue names no files, tests, or entry points. Start by reviewing the repository context and clarifying whether this is a proposed educational topic or an implementation task; done requires an agreed scope for the JavaScript piano and its tuning behavior.

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