Quality checks specific to generated footage

Use this only for the final assembled delivery MP4, alongside video-quality; do not run it after each generated preview clip. video-quality covers what applies to every video this product makes: decode/duration/dimensions, black frames and freezes, legible text, a coherent edit, and a passing quality-report.json. Run it first and in full -- this skill does not repeat it.

What this skill adds is the failure modes a camera cannot produce, because they only exist in generated footage: a face that drifts across shots, a sixth finger, a background that reflows between frames, motion that snaps rather than continues across a cut. A technical pass and a coherent-edit pass both miss these, because nothing about them fails to decode, and nothing about them is a black frame.