Folders containing N audio files (one per chapter/part) get one parsedAudiobookFile per file; each file's chapter list is synthesized as a single chapter with title = filename stem. Title/author/series/ year come from the first file's tags. Also drops the duplicate pickFirstNonEmpty helper added in Task 6 in favor of the existing firstNonEmpty already in probe.go. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>