Book imports with no audio when tracks are named `.MP3` instead of `.mp3`

A book folder whose tracks came off an older Windows ripper are named Track 01.MP3. Importing through the books API or a watch folder either fails or produces a book with no audio at all, and nothing in the output points at the reason. Storyteller v2, self-hosted Docker.

Resolution: The isAudioFile check compares file extensions case-sensitively, so .MP3 doesn't match the audio extension list and every track is silently dropped - the import then either errors generically or yields an audio-less book. Until the case-insensitive check ships, lowercase the extensions before import, e.g. from the book folder run for f in *.MP3; do mv -- "$f" "${f%.MP3}.mp3"; done (or rename 's/\.MP3$/.mp3/' *.MP3). This applies to any uppercase audio extension, not just MP3, so normalize .M4B/.FLAC and friends the same way.