Thank you for playing and appreciating the low size, engine-less approach. :D
Regarding the sound, it should start playing after pressing a key (on the keyboard, while the game iframe is focused). It should had play after a mouse click, but I did not figure out why it did not and I was running out of time. Your comment helped me locate the issue - it seems I was just building upon my previous codebase of something that used a mouse and added e.preventDefault(); e.stopPropagation(); to mouse events on the canvas element, the consequence of which is that mouse clicks do nothing now (aside from being mouse button state being (somewhat) tracked in a variable, which is not even used for this game). Two important consequences are 1) sound not playing and 2) once focused out of the game iframe, it does not get focused back in after clicking it (gamepad still works, but keyboard will not), unless one goes to full screen and clicks outside of the game canvas.
So thank you for pointing this out, I will remove e.preventDefault(); e.stopPropagation(); for future projects (there is the contextmenu event anyway, which is supported for over a decade on all major browsers (except Safari). :)