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.CentralUI.PlaywrightTests/SiteCalls/SiteCallsPageTests.cs

@@ -282,8 +282,8 @@ public class SiteCallsPageTests
             // be relayed to the owning site. Unlike the display-only tests above,
             // this one actually relays to the owning site, so the SourceSite must
             // be a *real* site identifier from the running cluster (site-a) and
-            // not the cosmetic "plant-a" label: an unknown site has no registered
-            // ClusterClient, so CentralCommunicationActor drops the envelope
+            // not the cosmetic "plant-a" label: an unknown site has no reachable
+            // gRPC endpoint, so CentralCommunicationActor drops the envelope
             // without replying and the relay only resolves on the 10s inner Ask
             // timeout — too slow for the toast assertion below. Relayed to a live
             // site, the site finds no parked S&F message for this freshly-seeded
@@ -319,7 +319,7 @@ public class SiteCallsPageTests
             // We only assert that an outcome toast appears (exactly one — the
             // single-toast contract), not which one, since the live cluster
             // state determines the outcome. The wait is generous (15s): the
-            // relay round-trips to the site over ClusterClient, and a worst-case
+            // relay round-trips to the site over gRPC, and a worst-case
             // path can sit on the 10s inner relay timeout before the response —
             // and the toast itself auto-dismisses 5s after it appears, so the
             // assertion must catch it inside that window.