feat(adminui): IFleetDiagnosticsClient skeleton (Akka round-trip tracked as F17)

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Clients/FleetDiagnosticsClient.cs

@@ -0,0 +1,36 @@
+using Akka.Actor;
+using ZB.MOM.WW.OtOpcUa.Commons.Interfaces;
+using ZB.MOM.WW.OtOpcUa.Commons.Types;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Clients;
+
+/// <summary>
+/// <see cref="IFleetDiagnosticsClient"/> that targets a named node's <c>DriverHostActor</c> over
+/// Akka cluster <see cref="ActorSelection"/>.
+///
+/// The actual <c>GetDiagnosticsRequest</c>/<c>NodeDiagnosticsSnapshot</c> round-trip on the
+/// driver side is staged for follow-up F17 (depends on DriverHostActor exposing the request
+/// handler; right now it only handles DispatchDeployment). For now the client returns an empty
+/// snapshot so the UI can render a "no data yet" state.
+/// </summary>
+public sealed class FleetDiagnosticsClient : IFleetDiagnosticsClient
+{
+    private readonly ActorSystem _system;
+
+    public FleetDiagnosticsClient(ActorSystem system)
+    {
+        _system = system;
+    }
+
+    public Task<NodeDiagnosticsSnapshot> GetDiagnosticsAsync(NodeId nodeId, CancellationToken ct)
+    {
+        // F17: ActorSelection at $"akka.tcp://{system}@{nodeId.Value}:4053/user/driver-host"
+        // → Ask<NodeDiagnosticsSnapshot>(new GetDiagnostics(), timeout).
+        var snapshot = new NodeDiagnosticsSnapshot(
+            nodeId,
+            CurrentRevision: null,
+            Drivers: Array.Empty<DriverInstanceDiagnostics>(),
+            AsOfUtc: DateTime.UtcNow);
+        return Task.FromResult(snapshot);
+    }
+}