Overlapping clips sum linearly in mix_audio_montage and can exceed full
scale (two hot clips reach +/-2; gain > 1 would too); the cpal sink
forwarded samples unclamped, so overlaps clipped at the DAC. Clamp the
accumulator after the montage mix (both the heap and shm-slot paths
share mix_audio_montage) and document it on render_audio_samples.
Mike-Solar
e128a6aca1