Extract the demo's request-scoped SDK compatibility port #1523

Port the existing demo callers to one exact public reviewed EdgeZero integration revision, preserving current body/head ownership, immutable ingress, incoming shared HTTP client, cancellation, explicit caller deadlines and managed Fastly delivery. Remove the replaced raw adapter transports without creating a fallback transport, extra timer or result ledger.

This is the scoped demo extraction, not the independent broad cutover/qualification initiative. New buffer-group, codec-subset, phase-timeout, TLS/cap policy and relay/privacy development remain outside this task. Related original integration: #1424.