R1.3 GetServerTimeZoneAsync over gRPC (live-verified); R1.4 bounded out on gRPC

Live-probed both R1.3 and R1.4 against a real 2023 R2 server over the gRPC
StatusService; implemented the one that carries an evidence-backed value.

R1.3 GetServerTimeZoneAsync — SHIPPED:
- StatusService.GetSystemTimeZoneName(uiHandle) returns the real server zone
  over RemoteGrpc (the 2020 WCF op is a client-side stub returning empty).
- HistorianGrpcStatusClient.GetSystemTimeZoneNameAsync -> dialect routing ->
  public HistorianClient.GetServerTimeZoneAsync. Non-gRPC transports fail
  closed with ProtocolEvidenceMissingException (no empty-string lie).
- Golden message-shape unit test + non-gRPC guardrail unit test + gated live
  test. 271 unit tests pass.

R1.4 GetHistorianInfoAsync (EventStorageMode) — bounded out on gRPC too:
- gRPC GetHistorianInfo is the same named-value query as 2020 WCF (only
  HistorianVersion resolves); EventStorageMode + 7 variants fail on both
  GetHistorianInfo and GetSystemParameter. The 518-byte struct is filled by a
  native vtable+648 HCAL call, not the gRPC op (per the 2023 R2 decompile), so
  the field is never on the wire. Not shipped on any transport. Closes the
  roadmap's open "build against a live 2023 R2 server" caveat.

Also correct the stale M3 roadmap section: D2 already proved
Transaction.AddNonStreamValues* rides the storage-engine pipe (STransactPipeClient2
-> aaStorageEngine), not WCF — same wall as R4.2 — so M3-over-WCF is blocked, not
"the path that is NOT the gated cache push".

Docs: hcal-roadmap.md, wcf-historian-info.md, wcf-status-localhost.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs

@@ -69,6 +69,21 @@ internal sealed class Historian2020ProtocolDialect
             : Wcf.HistorianWcfStatusClient.GetSystemParameterAsync(_options, name, cancellationToken);
     }
 
+    public Task<string?> GetServerTimeZoneAsync(CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+
+        // 2023 R2 gRPC returns the real server time-zone name; the 2020 WCF
+        // GetSystemTimeZoneName is a client-side stub (empty value), so there is no evidence-backed
+        // value to return on that transport — fail closed rather than hand back an empty string.
+        if (!UseGrpc)
+        {
+            throw new ProtocolEvidenceMissingException("GetSystemTimeZoneName (2020 WCF stub — gRPC/2023R2 only)");
+        }
+
+        return HistorianGrpcStatusClient.GetSystemTimeZoneNameAsync(_options, cancellationToken);
+    }
+
     public Task<string?> GetRuntimeParameterAsync(string name, CancellationToken cancellationToken)
     {
         cancellationToken.ThrowIfCancellationRequested();