clients/dotnet: SDK methods for AcknowledgeAlarm + QueryActiveAlarms (PR E.2)

Seventh PR of the alarms-over-gateway epic
(docs/plans/alarms-over-gateway.md). Depends on PR A.1 (proto, merged)
and E.1 (regen, merged).

Hand-written .NET SDK methods on top of the regenerated proto types:

- MxGatewayClient.AcknowledgeAlarmAsync — routes through the existing
  safe-unary retry pipeline (Acks are idempotent at MxAccess), maps
  Unauthenticated/PermissionDenied RpcExceptions to typed
  MxGatewayAuthenticationException / MxGatewayAuthorizationException
  via GrpcMxGatewayClientTransport.MapRpcException.
- MxGatewayClient.QueryActiveAlarmsAsync — server-streaming
  IAsyncEnumerable<ActiveAlarmSnapshot> mirroring the StreamEvents
  pattern.
- IMxGatewayClientTransport extended; GrpcMxGatewayClientTransport
  implements both methods using the regenerated grpc client.
- FakeGatewayTransport extended with capture lists, exception queue,
  and reply / snapshot enqueue helpers.

CLI version-string assertions updated for the GatewayProtocolVersion
2 → 3 bump from A.1.

The CLI alarms verb (subscribe / acknowledge / query-active) is
deferred to a follow-up — keeping this PR focused on the SDK surface
that lmxopcua's GalaxyDriver consumes in PR B.2. The other-language
SDKs (E.3-E.6) layer the same shape on the regen.

Tests:
- 6 new MxGatewayClientAlarmsTests — request shape, cancellation
  honor (linked-token via retry pipeline), Unauthenticated mapping,
  streaming snapshot enumeration, filter prefix passthrough,
  cancellation during enumeration.
- Full client test suite: 57 passed (was 51; 6 new).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs

@@ -116,6 +116,65 @@ internal sealed class GrpcMxGatewayClientTransport(
         return StreamEventsAsync(request, callOptions);
     }
 
+    /// <inheritdoc />
+    public async Task<AcknowledgeAlarmReply> AcknowledgeAlarmAsync(
+        AcknowledgeAlarmRequest request,
+        CallOptions callOptions)
+    {
+        try
+        {
+            return await RawClient.AcknowledgeAlarmAsync(request, callOptions)
+                .ResponseAsync
+                .ConfigureAwait(false);
+        }
+        catch (RpcException exception)
+        {
+            throw MapRpcException(exception, callOptions.CancellationToken);
+        }
+    }
+
+    /// <inheritdoc />
+    public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
+        QueryActiveAlarmsRequest request,
+        CallOptions callOptions,
+        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+        CancellationToken effectiveCancellationToken = cancellationToken.CanBeCanceled
+            ? cancellationToken
+            : callOptions.CancellationToken;
+
+        using AsyncServerStreamingCall<ActiveAlarmSnapshot> call = RawClient.QueryActiveAlarms(request, callOptions);
+
+        IAsyncStreamReader<ActiveAlarmSnapshot> responseStream = call.ResponseStream;
+        while (true)
+        {
+            ActiveAlarmSnapshot? snapshot;
+            try
+            {
+                if (!await responseStream.MoveNext(effectiveCancellationToken).ConfigureAwait(false))
+                {
+                    break;
+                }
+
+                snapshot = responseStream.Current;
+            }
+            catch (RpcException exception)
+            {
+                throw MapRpcException(exception, effectiveCancellationToken);
+            }
+
+            yield return snapshot;
+        }
+    }
+
+    /// <inheritdoc />
+    IAsyncEnumerable<ActiveAlarmSnapshot> IMxGatewayClientTransport.QueryActiveAlarmsAsync(
+        QueryActiveAlarmsRequest request,
+        CallOptions callOptions)
+    {
+        return QueryActiveAlarmsAsync(request, callOptions);
+    }
+
     private static Exception MapRpcException(
         RpcException exception,
         CancellationToken cancellationToken)