feat(host): register SiteCallAuditActor + CachedCallTelemetry forwarder/bridge (#22, #23 M3)

M3 Bundle F (Task F1) wires the cached-call audit pipeline through the
composition roots:

- Central: register SiteCallAuditActor as a cluster singleton + proxy
  (mirrors AuditLogIngestActor and NotificationOutboxActor). Program.cs
  calls .AddSiteCallAudit() on the central role.
- Site: register ICachedCallTelemetryForwarder + CachedCallLifecycleBridge
  in AddAuditLog (lazy factory — Central nodes degrade to audit-only
  emission because IOperationTrackingStore is site-only).
- Site: bind CachedCallLifecycleBridge to ICachedCallLifecycleObserver so
  StoreAndForwardService picks it up via DI.
- Site: introduce IStoreAndForwardSiteContext + Host adapter to surface the
  site id to StoreAndForwardService without creating a
  StoreAndForward -> HealthMonitoring project-reference cycle.
- ScriptExecutionActor resolves ICachedCallTelemetryForwarder per script
  scope and threads it into ScriptRuntimeContext.

CachedCallTelemetryForwarder's IOperationTrackingStore dependency is now
nullable so Central DI validation succeeds with the lazy registration; the
forwarder's tracking-half emission is a no-op when the store is absent.

Tests:
- AkkaHostedServiceAuditWiringTests: Central host builds with
  AddSiteCallAudit and resolves ICachedCallTelemetryForwarder; Site
  resolves the forwarder + bridge + observer + IStoreAndForwardSiteContext.
- Full solution: 194 Host tests green, 241 SiteRuntime tests green, every
  other suite unchanged.

src/ScadaLink.Host/SiteServiceRegistration.cs

@@ -42,6 +42,14 @@ public static class SiteServiceRegistration
         var siteDbPath = config["ScadaLink:Database:SiteDbPath"] ?? "site.db";
         services.AddSiteRuntime($"Data Source={siteDbPath}");
         services.AddDataConnectionLayer();
+        // Audit Log #23 (M3 Bundle F): adapter that surfaces the site id to
+        // StoreAndForwardService through DI WITHOUT introducing a
+        // StoreAndForward → HealthMonitoring project-reference cycle. Must be
+        // registered BEFORE AddStoreAndForward so the S&F factory resolves a
+        // non-empty SiteId at construction time (otherwise the S&F service is
+        // a singleton and the empty-string value would be cached for the
+        // lifetime of the process).
+        services.AddSingleton<ScadaLink.StoreAndForward.IStoreAndForwardSiteContext, StoreAndForwardSiteContext>();
         services.AddStoreAndForward();
         services.AddSiteEventLogging();