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.Commons/Messages/Audit/SiteCallRelayMessages.cs

@@ -28,7 +28,7 @@ public enum SiteCallRelayOutcome
     NotParked,
 
     /// <summary>
-    /// The owning site could not be reached (offline / no ClusterClient route /
+    /// The owning site could not be reached (offline / no route to the site /
     /// relay timed out). The action was NOT applied; the operator may retry once
     /// the site is back online.
     /// </summary>