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.SiteCallAudit/SiteCallAuditActor.cs

@@ -164,7 +164,7 @@ public class SiteCallAuditActor : ReceiveActor
     /// <summary>
     /// The central→site command transport — the
     /// <c>CentralCommunicationActor</c>, which owns the per-site
-    /// <c>ClusterClient</c> map and routes a <see cref="SiteEnvelope"/> to the
+    /// transport map and routes a <see cref="SiteEnvelope"/> to the
     /// owning site. Set via <see cref="RegisterCentralCommunication"/> by the
     /// Host after both actors exist (this actor is a cluster singleton; the
     /// transport actor is created separately). Null until registration
@@ -1079,7 +1079,7 @@ public class SiteCallAuditActor : ReceiveActor
     /// <c>SiteCalls</c> mirror row. It wraps a <see cref="RetryParkedOperation"/>
     /// in a <see cref="SiteEnvelope"/> addressed to <c>SourceSite</c>, Asks the
     /// <c>CentralCommunicationActor</c> (which routes it over the per-site
-    /// <c>ClusterClient</c>), and maps the site's
+    /// gRPC transport), and maps the site's
     /// <see cref="ParkedOperationActionAck"/> — or an Ask timeout — onto a
     /// <see cref="RetrySiteCallResponse"/>. A timeout / no-route is reported as
     /// the distinct <see cref="SiteCallRelayOutcome.SiteUnreachable"/> outcome,

src/ZB.MOM.WW.ScadaBridge.SiteCallAudit/SiteCallAuditOptions.cs

@@ -30,7 +30,7 @@ public class SiteCallAuditOptions
     /// Ask timeout for the central→site Retry/Discard relay. When
     /// the owning site does not ack a <c>RetryParkedOperation</c> /
     /// <c>DiscardParkedOperation</c> within this window — site offline, no
-    /// ClusterClient route, or central buffering deliberately absent — the relay
+    /// route to the site, or central buffering deliberately absent — the relay
     /// reports a <c>SiteUnreachable</c> outcome. Default 10 seconds: long enough
     /// to absorb a healthy cross-cluster round-trip, short enough that an
     /// operator clicking Retry on an offline site gets a fast, honest answer.