Cliff/edge spectral detector with a confidence score; effective cutoff =
cliff if confident else sr/2 (covers band-limited, full-band, and genuine
low-rate files in one rule). Round down to the nearest supported Nyquist.
Adds an "auto" dropdown option (default). Validated empirically before design.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
