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.

tests/ZB.MOM.WW.ScadaBridge.SiteCallAudit.Tests/SiteCallRelayTests.cs

@@ -164,7 +164,7 @@ public class SiteCallRelayTests : TestKit
     public void RetrySiteCall_SiteNeverReplies_ReportsSiteUnreachable()
     {
         // A central comm probe that silently drops the relay — models an offline
-        // site / no ClusterClient route: the Ask times out.
+        // site / no route to the site: the Ask times out.
         var central = CreateTestProbe();
         var actor = CreateActor(central.Ref);