- mustAuth: print 'requesting photo library access...' / 'access granted'
- cmdBackupAll: print 'loading photo library tree...' / 'found N albums'
- cmdExport: print 'loading assets...' / 'exporting N assets (mode)...'
- backupTree: print 'album: Name (N assets)' per album
- exportAssetsParallel: slot-based progress shows each asset as it completes
instead of waiting for all to finish
- Fix data race: use jobs channel instead of shared range iteration