Removed stale Loom link and old checkpoint-diff screenshot reference.
README now references 3 new screenshots matching the current product:
LineagePage dashboard, CLI state+metrics, checkpoint detail with
structured tasks and notes. Screenshots are placeholders until
captured from the live environment.
Added docs/DEMO_SCRIPT.md: 3-act, 4-5 minute recording script
covering the state surface, coordination proof (metrics + autonomy
milestone), and developer experience. Includes exact commands,
highlight points, and a screenshot capture checklist.
