New toggle under Post-Download Conversion: automatically converts 24-bit
or high sample rate FLAC files to 16-bit/44.1kHz after download, replacing
the original. Uses ffmpeg with temp file + verify + atomic swap for safety.
Runs before lossy copy so MP3s are made from the downsampled version.
Also prevents bit depth strict mode from rejecting files that will be
downsampled anyway.
a9d0607d25
