Build SLA demo fixtures from execution time in the viewer's zone

For clock-driven SLA demos, seed pickup instants relative to the fixture's execution time and evaluate them in the viewer's IANA time zone, not the server zone. Choose offsets on both sides of every threshold so the fixture covers starts-later, on-track, approaching, and overdue states. Record the reference instant and viewer zone with the fixture. Because an approaching-state example crosses its boundary as time advances, label it as ephemeral or freeze the clock for deterministic acceptance tests.