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/ISiteCommandTransport.cs

@@ -4,13 +4,11 @@ namespace ZB.MOM.WW.ScadaBridge.Communication.Actors;
 
 /// <summary>
 /// The central→site command-send seam, injected into <see cref="CentralCommunicationActor"/>
-/// below the <see cref="SiteEnvelope"/> handler. Exactly one implementation is active per node,
-/// chosen by <c>ScadaBridge:Communication:SiteTransport</c>:
-/// <list type="bullet">
-///   <item><see cref="AkkaSiteTransport"/> — today's per-site <c>ClusterClient</c> path (default).</item>
-///   <item><see cref="ZB.MOM.WW.ScadaBridge.Communication.Grpc.GrpcSiteTransport"/> — the site
-///     <c>SiteCommandService</c> gRPC plane.</item>
-/// </list>
+/// below the <see cref="SiteEnvelope"/> handler. The sole implementation is
+/// <see cref="ZB.MOM.WW.ScadaBridge.Communication.Grpc.GrpcSiteTransport"/>, over the site
+/// <c>SiteCommandService</c> gRPC plane. The seam predates that: it was introduced so the Akka
+/// <c>ClusterClient</c> path and the gRPC plane could run side by side during the migration, and
+/// is kept because it is the natural substitution point for tests.
 /// The producers above the seam (<c>CommunicationService</c>'s 27 commands, <c>SiteCallAuditActor</c>'s
 /// 2 parked relays, and <c>DebugStreamBridgeActor</c>'s subscribe/unsubscribe) are unchanged — they
 /// still <c>Ask</c>/<c>Tell</c> a <see cref="SiteEnvelope"/> to the actor, which delegates here.
@@ -27,14 +25,14 @@ public interface ISiteCommandTransport
     /// delivered to <paramref name="replyTo"/> — for an <c>Ask</c> that is the temporary ask actor
     /// (completing the caller's task); for a <c>Tell</c>-with-sender (the debug bridge) that is the
     /// originating actor. A message with no route (an unknown site) is warned and dropped so the
-    /// caller's <c>Ask</c> times out, exactly as today's ClusterClient path behaves.
+    /// caller's <c>Ask</c> times out — central never buffers for an unreachable site.
     /// </summary>
     /// <param name="envelope">The site-addressed command envelope.</param>
     /// <param name="replyTo">Where a reply (or a <see cref="Status.Failure"/>) is delivered.</param>
     void Send(SiteEnvelope envelope, IActorRef replyTo);
 
     /// <summary>
-    /// Reconciles per-site transport resources (ClusterClients for Akka, channel pairs for gRPC)
+    /// Reconciles per-site transport resources (gRPC channel pairs)
     /// against the freshly loaded site set. Called once per DB refresh tick with the same cache
     /// message the actor already receives — the ONE DB-poll loop feeds both transports.
     /// </summary>