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/StoreAndForwardSiteContext.cs

@@ -0,0 +1,32 @@
+using Microsoft.Extensions.Options;
+using ScadaLink.StoreAndForward;
+
+namespace ScadaLink.Host;
+
+/// <summary>
+/// Audit Log #23 (M3 Bundle F): Host-side adapter implementing the
+/// optional <see cref="IStoreAndForwardSiteContext"/> the Store-and-Forward
+/// service consults to stamp cached-call audit telemetry with the site id.
+/// </summary>
+/// <remarks>
+/// Forwards <see cref="NodeOptions.SiteId"/> verbatim — the same value
+/// <see cref="SiteIdentityProvider"/> exposes to HealthMonitoring. Defined as
+/// a separate adapter (rather than reusing <see cref="SiteIdentityProvider"/>)
+/// to avoid pulling HealthMonitoring into the StoreAndForward project's
+/// dependency graph, which would create a project-reference cycle.
+/// </remarks>
+public class StoreAndForwardSiteContext : IStoreAndForwardSiteContext
+{
+    public string SiteId { get; }
+
+    public StoreAndForwardSiteContext(IOptions<NodeOptions> nodeOptions)
+    {
+        // NodeOptions.SiteId is nullable; SiteServiceRegistration ONLY adds
+        // this binding on the site role, so a non-null site id is expected
+        // here. Mirror SiteIdentityProvider's hard fail so a missing site id
+        // surfaces at composition time rather than at the first cached call.
+        SiteId = nodeOptions.Value.SiteId
+            ?? throw new InvalidOperationException(
+                "ScadaLink:Node:SiteId is required for the site role's StoreAndForward wiring.");
+    }
+}