Add files recursively from file explorer to a cache

### Problem

The app doesn't automatically open my music

### Proposal

All my music files are in the music folder, each album is stored in a separate folder. The app should be able to have a default directory(s) and then checks it, in this case /home/mike/Music, and then just put all the files recursively inside a cache which is updated for new or removed entries.

### Prior Art (Optional)

_No response_