refactor(comm): retire ClusterClient naming after the gRPC cutover

Phase 4 of the ClusterClient -> gRPC migration deleted the Akka transports
but left the naming behind: `ClusterClientSiteAuditClient` was transport-
agnostic and worked unchanged, so it survived the deletion under a name
that now describes a transport the repo no longer has. Same for a scatter
of doc-comments still framing gRPC as "the new transport" beside an Akka
one that is gone.

Renames it to `SiteCommunicationAuditClient` (and its test file) and
rewrites the stale comments to describe the single transport that exists.
Also tightens CLAUDE.md: drops the self-describing directory listing and
the 27-component enumeration in favour of the non-obvious parts only.

Behaviour-neutral: names and prose only. Recorded as the Phase 4
follow-up in docs/plans/2026-07-22-clusterclient-to-grpc-plan.md.

src/ZB.MOM.WW.ScadaBridge.Communication/Actors/SiteCommunicationActor.cs

@@ -16,9 +16,10 @@ using ZB.MOM.WW.ScadaBridge.Commons.Messages.RemoteQuery;
 namespace ZB.MOM.WW.ScadaBridge.Communication.Actors;
 
 /// <summary>
-/// Site-side actor that receives messages from central via ClusterClient and routes
-/// them to the appropriate local actors. Also sends heartbeats and health reports
-/// to central via the registered ClusterClient.
+/// Site-side actor that receives messages from central over the site-hosted
+/// <c>SiteCommandService</c> gRPC plane and routes them to the appropriate local actors.
+/// Also sends heartbeats and health reports to central over its
+/// <see cref="ICentralTransport"/> (<see cref="Grpc.GrpcCentralTransport"/> in production).
 ///
 /// Routes all 8 message patterns to local handlers.
 /// </summary>
@@ -157,15 +158,15 @@ public class SiteCommunicationActor : ReceiveActor, IWithTimers
         // the SITE-SPECIFIC role, because that is what site singletons (the Deployment
         // Manager) are placed on. Either node may receive this (the actor is per-node, not a
         // singleton, and contact rotation picks whichever answers); the target is resolved
-        // from cluster state, not from who received the message. Over ClusterClient the ack
-        // Tell merely enqueues, so the dispatcher resolves-and-leaves in one step (the gRPC
-        // transport defers the leave to keep ack-before-Leave — see PrepareFailover).
+        // from cluster state, not from who received the message. The gRPC transport defers the
+        // leave to keep ack-before-Leave — see PrepareFailover. (Under the removed ClusterClient
+        // path the ack Tell merely enqueued, so the dispatcher resolved-and-left in one step.)
         Receive<TriggerSiteFailover>(msg => Sender.Tell(_dispatcher.HandleFailover(msg)));
 
-        // The seven site→central sends now delegate to the injected transport (ClusterClient by
-        // default, gRPC when configured). Each handler captures the current Sender as the reply
-        // target so central's reply routes straight back to the waiting Ask, not through this
-        // actor — the exact sender-forwarding the ClusterClient path relied on. The per-message
+        // The seven site→central sends delegate to the injected transport (GrpcCentralTransport in
+        // production). Each handler captures the current Sender as the reply target so central's
+        // reply routes straight back to the waiting Ask, not through this actor — preserving the
+        // sender-forwarding the original ClusterClient path relied on. The per-message
         // "no transport / not-accepted" fallbacks live inside the transport now.
 
         // Notification Outbox: forward a buffered notification (S&F forwarder's Ask → ack back).
@@ -229,9 +230,9 @@ public class SiteCommunicationActor : ReceiveActor, IWithTimers
     /// Executes a resolved command route within the actor: Forward to the target (preserving the
     /// central Ask sender so the reply routes straight back to the waiting Ask), or — when a
     /// null-guarded handler is unregistered — Tell the caller the dispatcher's synthetic reply.
-    /// The fire-and-forget disposition (UnsubscribeDebugView) is a plain Forward here, exactly as
-    /// before: over ClusterClient the site never acked it, so the synthetic ack is a gRPC-only
-    /// concern.
+    /// The fire-and-forget disposition (UnsubscribeDebugView) is a plain Forward here: the site
+    /// never acked it under the original ClusterClient path either, so the synthetic ack is a
+    /// gRPC-only concern.
     /// </summary>
     /// <param name="command">The migrated central→site command to route.</param>
     private void DispatchCommand(object command)