Improve behavior when multiple directories/tracks have the same ID

[azuline]

Can occur in the event of a bad bug--my attempt to run this system on MacOS and its terrible handling of diacritics fucked my library up a bit. also seeing this when syncthing gets confused during track renames across machines, some tracks get duplicated.

cases to test:

• directory has two .rose.xxx.toml files -> should then keep the one with the ID of the audio tags
• two directories have the same ID -> ???
• two tracks have the same ID -> ???