Add cover image detection for audio files in scanner

During scanning, when an audio file is found in a directory that also
contains an image file (jpg/png/gif), the scanner now assigns that image
as the audio file's thumbnail_path. This is common for audiobooks which
have cover.jpg alongside the audio files.

Changes:
- scanner: two-pass walk to collect sibling images, then pair with audio
- CSS: add .row-cover style for audio items with covers
- JS: render audio rows with cover images when thumbnail_path is set

0 files changed, 0 insertions, 0 deletions