fix(health): site /health/active uses the shared role-scoped ActiveNodeHealthCheck (ScadaBridge#97)

Replace the private SitePairActiveNodeHealthCheck (503 whenever no ActorSystem, no data)
with the shared ZB.MOM.WW.Health ActiveNodeHealthCheck constructed with the site-{SiteId}
role: Degraded (200) during startup per the Health spec, and it publishes
selfAddress/activeRole/activeNode so the Overview dashboard can name the active site node.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

docs/requirements/Component-Host.md

@@ -231,7 +231,7 @@ verdict of the `active-node` probe (register row 71).
 
 `DefaultHealthCheckService` logs one line per check per probe and picks the level from the verdict —
 Debug / Warning / **Error** for Healthy / Degraded / Unhealthy. Both active-node checks
-(`SitePairActiveNodeHealthCheck` on a site, the shared `ActiveNodeHealthCheck` on central) answer
+(the shared `ActiveNodeHealthCheck`, role-scoped to `site-{SiteId}` on a site and unscoped on central) answer
 Unhealthy on the standby, because 503 is exactly the contract `/health/active` publishes to Traefik
 and the family dashboard. A perfectly healthy standby therefore logged ERR on every probe — every
 10 s on a site node, every 5 s on a central node behind Traefik's active-node probe — which floods