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.Tests/FakeGatewayTransport.cs

@@ -41,6 +41,24 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     /// </summary>
     public List<(StreamEventsRequest Request, CallOptions CallOptions)> StreamEventsCalls { get; } = [];
 
+    /// <summary>
+    /// Gets the list of captured AcknowledgeAlarmAsync calls.
+    /// </summary>
+    public List<(AcknowledgeAlarmRequest Request, CallOptions CallOptions)> AcknowledgeAlarmCalls { get; } = [];
+
+    /// <summary>
+    /// Gets the list of captured QueryActiveAlarmsAsync calls.
+    /// </summary>
+    public List<(QueryActiveAlarmsRequest Request, CallOptions CallOptions)> QueryActiveAlarmsCalls { get; } = [];
+
+    /// <summary>
+    /// Gets the queue of exceptions to throw from AcknowledgeAlarmAsync.
+    /// </summary>
+    public Queue<Exception> AcknowledgeAlarmExceptions { get; } = new();
+
+    private readonly Queue<AcknowledgeAlarmReply> _acknowledgeReplies = new();
+    private readonly List<ActiveAlarmSnapshot> _activeAlarmSnapshots = [];
+
     /// <summary>
     /// Gets or sets the reply to return from OpenSessionAsync.
     /// </summary>
@@ -168,4 +186,57 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     {
         _events.Add(gatewayEvent);
     }
+
+    /// <summary>
+    /// Records the acknowledge call and returns the next enqueued reply (or default).
+    /// </summary>
+    public Task<AcknowledgeAlarmReply> AcknowledgeAlarmAsync(
+        AcknowledgeAlarmRequest request,
+        CallOptions callOptions)
+    {
+        AcknowledgeAlarmCalls.Add((request, callOptions));
+        if (AcknowledgeAlarmExceptions.TryDequeue(out Exception? exception))
+        {
+            throw exception;
+        }
+
+        return Task.FromResult(_acknowledgeReplies.Count > 0
+            ? _acknowledgeReplies.Dequeue()
+            : new AcknowledgeAlarmReply
+            {
+                SessionId = request.SessionId,
+                CorrelationId = request.ClientCorrelationId,
+                ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
+                Status = new MxStatusProxy { Success = 1, Category = MxStatusCategory.Ok },
+            });
+    }
+
+    /// <summary>
+    /// Records the query call and yields each enqueued snapshot.
+    /// </summary>
+    public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
+        QueryActiveAlarmsRequest request,
+        CallOptions callOptions)
+    {
+        QueryActiveAlarmsCalls.Add((request, callOptions));
+
+        foreach (ActiveAlarmSnapshot snapshot in _activeAlarmSnapshots)
+        {
+            callOptions.CancellationToken.ThrowIfCancellationRequested();
+            await Task.Yield();
+            yield return snapshot;
+        }
+    }
+
+    /// <summary>Enqueues an acknowledge reply.</summary>
+    public void AddAcknowledgeReply(AcknowledgeAlarmReply reply)
+    {
+        _acknowledgeReplies.Enqueue(reply);
+    }
+
+    /// <summary>Enqueues a snapshot to be yielded from QueryActiveAlarmsAsync.</summary>
+    public void AddActiveAlarmSnapshot(ActiveAlarmSnapshot snapshot)
+    {
+        _activeAlarmSnapshots.Add(snapshot);
+    }
 }