fix(probe): Galaxy gRPC ping — drop invalid Retry, treat MxGatewayAuth exceptions as reachable (live /run)

Two bugs caught by live verification against the mxaccessgw at 10.100.0.48:5120:
- MaxAttempts=1 produced an invalid Polly RetryStrategyOptions -> the probe failed
  on every real gateway. Removed the Retry override (matches GalaxyDriver); fail-fast
  is already guaranteed by the TCP preflight + the per-call deadline.
- A rejected key surfaces as a typed MxGatewayAuthenticationException, not a raw
  RpcException, so 'auth-rejection = reachable' was bypassed. Catch the typed auth/
  authorization exceptions -> Ok=true.
Adds DriverProbeHandshakeE2eTests: direct-probe, skip-gated cross-protocol green/red
discrimination (Modbus, OpcUaClient, Galaxy + a local real OPC UA server).

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriverProbe.cs

@@ -101,6 +101,15 @@ public sealed class GalaxyDriverProbe : IDriverProbe
             var (ok, message) = ClassifyRpc(ex.StatusCode, host, port);
             return new(ok, message, ok ? sw.Elapsed : null);
         }
+        catch (Exception ex) when (ex is MxGatewayAuthenticationException or MxGatewayAuthorizationException)
+        {
+            // The gateway authenticated/authorized our call and rejected the (unresolved /
+            // placeholder) key — the mxaccessgw client surfaces this as a typed exception, NOT a
+            // raw RpcException. It still PROVES a live gateway gRPC server answered, so auth
+            // rejection counts as reachable (the probe never resolves the real secret).
+            sw.Stop();
+            return new(true, "gateway reachable & speaking gRPC (auth not checked)", sw.Elapsed);
+        }
         catch (OperationCanceledException) when (ct.IsCancellationRequested)
         {
             // The caller cancelled (their own timeout / shutdown) — surface a timeout message.
@@ -169,9 +178,11 @@ public sealed class GalaxyDriverProbe : IDriverProbe
             CaCertificatePath = gw.CaCertificatePath,
             ConnectTimeout = budget,
             DefaultCallTimeout = budget,
-            // One shot — the probe must not spin on transient (Unavailable/DeadlineExceeded)
-            // retries; the linked deadline above bounds the whole call regardless.
-            Retry = new MxGatewayClientRetryOptions { MaxAttempts = 1 },
+            // Leave Retry at the client default (as GalaxyDriver does) — an explicit
+            // MaxAttempts=1 maps to 0 Polly retries, which Polly rejects as an invalid
+            // RetryStrategyOptions. Fast-fail is already guaranteed: the TCP preflight rejects
+            // unreachable hosts before the gRPC call, and the linked deadline caps the call to
+            // the probe budget regardless of retries.
         };
     }