feat: replace debug view polling with real-time SignalR streaming

The debug view polled every 2s by re-subscribing for full snapshots. Now a
persistent DebugStreamBridgeActor on central subscribes once and receives
incremental Akka stream events from the site, forwarding them to the Blazor
component via callbacks and to the CLI via a new SignalR hub at
/hubs/debug-stream. Adds `debug stream` CLI command with auto-reconnect.

src/ScadaLink.Host/Actors/AkkaHostedService.cs

@@ -185,6 +185,11 @@ akka {{
         var commService = _serviceProvider.GetService<CommunicationService>();
         commService?.SetCommunicationActor(centralCommActor);
 
+        // Wire up the DebugStreamService with the ActorSystem
+        var debugStreamService = _serviceProvider.GetService<DebugStreamService>();
+        debugStreamService?.SetActorSystem(_actorSystem!);
+
+
         // Management Service — accessible via ClusterClient
         var mgmtLogger = _serviceProvider.GetRequiredService<ILoggerFactory>()
             .CreateLogger<ScadaLink.ManagementService.ManagementActor>();