Add UI interaction sounds

[piqey]

I think these generally ought to be derived from Half-Life 2 or Counter-Strike: Source sound effects (via sound.Add). Experiment with pitch shifting and all other in-engine modifications we can do to native sound effects.

[piqey]

Technically made some progress with this in coderage-xyz/code-zs@5bda03d today, along with some other stuff for the F4 menu.