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/Program.cs

@@ -16,6 +16,7 @@ using ScadaLink.ManagementService;
 using ScadaLink.NotificationOutbox;
 using ScadaLink.NotificationService;
 using ScadaLink.Security;
+using ScadaLink.SiteCallAudit;
 using ScadaLink.TemplateEngine;
 using Serilog;
 
@@ -82,6 +83,12 @@ try
         // IAuditLogRepository. The site writer chain is still registered (lazy
         // singletons) but is never resolved on a central node.
         builder.Services.AddAuditLog(builder.Configuration);
+        // Site Call Audit (#22) — central node owns the SiteCallAuditActor
+        // singleton (M3 Bundle F). The extension itself currently registers
+        // nothing — actor Props are constructed inline in AkkaHostedService —
+        // but the call is here for symmetry with the other audit composition
+        // roots so future per-actor DI lands without touching Program.cs.
+        builder.Services.AddSiteCallAudit();
         builder.Services.AddTemplateEngine();
         builder.Services.AddDeploymentManager();
         builder.Services.AddSecurity();