[Feature Request] Dynamic population of custom sounds

[mr-ransel]

I love this! It's super clean and well executed. Definitely going to be the new white noise generator for my son.

For running my own copy of this at home, it would be handy if it could list the mp3s in a particular folder (custom or some such, or just all the data folders), and if there are files that aren't covered by the existing tsx files describing the sound, populate them into the UI with a generic icon or into the custom category

This way adding in our own sounds would be as easy as adding a docker volume mount, and not having to edit tsx files each time.

To keep it from hitting disk constantly you could just do it once in startup, or add a "reload from disk" button

I figured this would cut down on people asking for the addition of other extraneous signs. (like a heartbeat sound in my case)