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.Communication/ServiceCollectionExtensions.cs

@@ -10,6 +10,7 @@ public static class ServiceCollectionExtensions
             .BindConfiguration("Communication");
 
         services.AddSingleton<CommunicationService>();
+        services.AddSingleton<DebugStreamService>();
 
         return services;
     }