Add ffmpeg to the Docker image so ffprobe can read each video/audio
file's duration server-side. Results are cached to a small persistent
per-course JSON file keyed by (relative path, size, mtime), so a file
only gets probed once - a container restart or the library scan's
in-memory cache expiring never re-runs ffprobe on unchanged files.
Course cards in the library browser (grid, list, and search) now show
total runtime alongside the media-file count, so you know the time
commitment before opening a course. Durations under a minute are
suppressed rather than showing a noisy "0m".
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
rmsitzandClaude Sonnet 5