Point the .NET client at the StreamAlarms alarm feed

Replace the client's QueryActiveAlarmsAsync with StreamAlarmsAsync —
a session-less subscription to the gateway's central alarm feed that
yields the active-alarm snapshot followed by live transitions.
AcknowledgeAlarm is session-less (AcknowledgeAlarmRequest no longer
carries a session id). Updates the transport interface, the gRPC
transport, the test fake, and the alarm tests; the .NET client
solution builds and its alarm tests pass.

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

clients/dotnet/MxGateway.Client/IMxGatewayClientTransport.cs

@@ -66,13 +66,13 @@ internal interface IMxGatewayClientTransport
         CallOptions callOptions);
 
     /// <summary>
-    /// Streams a snapshot of all alarms currently in Active or ActiveAcked state — the
-    /// ConditionRefresh equivalent for the gateway.
+    /// Attaches to the gateway's central alarm feed — the current active-alarm
+    /// snapshot followed by live transitions.
     /// </summary>
-    /// <param name="request">The query request, optionally scoped by alarm-reference prefix.</param>
+    /// <param name="request">The stream request, optionally scoped by alarm-reference prefix.</param>
     /// <param name="callOptions">gRPC call options.</param>
-    /// <returns>An async enumerable of active-alarm snapshots.</returns>
-    IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    /// <returns>An async enumerable of alarm feed messages.</returns>
+    IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CallOptions callOptions);
 }