site(status): public service-status surface — ORB and AMS fleet heartbeats and uptime

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Problem

The hosted review and testing services run on dedicated infrastructure, but there is no public surface showing that fleet's live state. A status page serves tenants (is the service up?) and makes the operational footprint legible to anyone evaluating the project.

Scope

• Public status page: ORB review service, AMS testing service, discovery-index — heartbeat, recent uptime, and incident history per component
• Reuses the existing health/alerting instrumentation (PagerDuty-integrated) as the data source; no new probes unless a component lacks one
• Builds on the fleet-health aggregation design in Design: fleet-wide health aggregation and status-page concept for hosted AMS #5226 where applicable; this issue is the public-surface slice
• No internal details beyond component name + status + uptime (no host names, no capacity data)

Acceptance

A public URL answers "is the service healthy and has it been?" per component; incidents appear without manual posting.

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JSO-6808