- LosslessConversionQuality model with bit depth/sample rate caps,
applied only when they reduce source quality
- FFmpegService probes sample rate and appends codec-specific args
(-ar, -sample_fmt, -bits_per_raw_sample) for FLAC/ALAC/WAV/AIFF
- Batch + single-track convert sheets expose quality cap options
- Persist real converted bit depth/sample rate to history/library DB
- track_metadata: recognize and convert to WAV/AIFF targets
- convertedAudioQualityLabel reflects actual output quality