feat(adminui): FleetStatusSignalRBridge — DPS → SignalR forwarding (F16)

New per-admin-node actor that subscribes to the fleet-status DistributedPubSub
topic + forwards every FleetStatusChanged snapshot to all SignalR clients
connected to FleetStatusHub via IHubContext.

Wired via WithOtOpcUaSignalRBridges (new AkkaConfigurationBuilder extension in
AdminUI.Hubs) — Program.cs calls it inside the if(hasAdmin) block alongside
WithOtOpcUaControlPlaneSingletons.

Per-node subscription rather than cluster-singleton: every admin node forwards
its own snapshots to its own connected clients. Simpler than singleton
coordination + acceptable because the messages are small and SignalR fan-out
is per-node anyway.

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -44,7 +44,10 @@ builder.Services.AddAkka("otopcua", (ab, sp) =>
 {
     ab.WithOtOpcUaClusterBootstrap(sp);
     if (hasAdmin)
+    {
         ab.WithOtOpcUaControlPlaneSingletons();
+        ab.WithOtOpcUaSignalRBridges();
+    }
     if (hasDriver)
         ab.WithOtOpcUaRuntimeActors();
 });