External library - Auto-scan when new files are added

[RobbWatershed]

Make the app auto-detect and auto-scan newly added files to the external library

https://developer.android.com/reference/android/os/FileObserver (File only)

https://stackoverflow.com/questions/75517788/is-there-some-way-to-listen-for-changes-under-a-tree-uri-on-saf