Probe each album exactly once and thread the ProbeResult through for
tags, quality, and format instead of hardcoding LibraryItem.format to
"FLAC" and re-probing on the tag-fallback path. Also skip album-level
directories starting with "." (previously only artist-level dirs were
skipped).
Adds the AudioProbe seam (probe.py, _probe.py MutagenProbe with a lazy
mutagen import, FakeAudioProbe) and scan_library, which walks /music,
resolves each album against MusicBrainz (falling back to embedded tags
when the folder name doesn't resolve), and idempotently records matched
albums as have (LibraryItem), monitored (MonitoredRelease, fulfilled),
and followed (WatchedArtist, autoMonitorFuture=false).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>