feat: add undo, improved menus, clear also resets time

[TN1ck]

CleanShot.2024-08-25.at.00.48.42.mp4

• Adds the undo feature, it can be triggered with the "undo" button or cmd/ctrl+z
• When using a keyboard, redo is also available with cmd/ctrl+y
• Improved the menu, so that it looks better on mobile and moved New/Clear to the top
• Shortcuts are not shown on very small displays (as a keyboard is most likely not present)

[TN1ck]

Fixes #10

[mgrider]

Well done. Not sure I've ever looked at such clear/readable javascript. 😂