feat: update DebugStreamBridgeActor to use gRPC for streaming events

After receiving the initial snapshot via ClusterClient, the bridge actor
now opens a gRPC server-streaming subscription via SiteStreamGrpcClient
for ongoing AttributeValueChanged/AlarmStateChanged events. Adds NodeA/
NodeB failover with max 3 retries, retry count reset on successful event,
and IWithTimers-based reconnect scheduling.

- DebugStreamBridgeActor: gRPC stream after snapshot, reconnect state machine
- DebugStreamService: inject SiteStreamGrpcClientFactory, resolve gRPC addresses
- ServiceCollectionExtensions: register SiteStreamGrpcClientFactory singleton
- SiteStreamGrpcClient: make SubscribeAsync/Unsubscribe virtual for testability
- SiteStreamGrpcClientFactory: make GetOrCreate virtual for testability
- New test suite: DebugStreamBridgeActorTests (8 tests)

src/ScadaLink.Communication/DebugStreamService.cs

@@ -5,6 +5,7 @@ using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Messages.DebugView;
 using ScadaLink.Communication.Actors;
+using ScadaLink.Communication.Grpc;
 
 namespace ScadaLink.Communication;
 
@@ -17,6 +18,7 @@ public class DebugStreamService
 {
     private readonly CommunicationService _communicationService;
     private readonly IServiceProvider _serviceProvider;
+    private readonly SiteStreamGrpcClientFactory _grpcClientFactory;
     private readonly ILogger<DebugStreamService> _logger;
     private readonly ConcurrentDictionary<string, IActorRef> _sessions = new();
     private ActorSystem? _actorSystem;
@@ -24,10 +26,12 @@ public class DebugStreamService
     public DebugStreamService(
         CommunicationService communicationService,
         IServiceProvider serviceProvider,
+        SiteStreamGrpcClientFactory grpcClientFactory,
         ILogger<DebugStreamService> logger)
     {
         _communicationService = communicationService;
         _serviceProvider = serviceProvider;
+        _grpcClientFactory = grpcClientFactory;
         _logger = logger;
     }
 
@@ -56,6 +60,8 @@ public class DebugStreamService
         // Resolve instance → unique name + site
         string instanceUniqueName;
         string siteIdentifier;
+        string grpcNodeAAddress;
+        string grpcNodeBAddress;
 
         using (var scope = _serviceProvider.CreateScope())
         {
@@ -69,6 +75,10 @@ public class DebugStreamService
 
             instanceUniqueName = instance.UniqueName;
             siteIdentifier = site.SiteIdentifier;
+            grpcNodeAAddress = site.GrpcNodeAAddress
+                ?? throw new InvalidOperationException($"Site {siteIdentifier} has no GrpcNodeAAddress configured.");
+            grpcNodeBAddress = site.GrpcNodeBAddress
+                ?? throw new InvalidOperationException($"Site {siteIdentifier} has no GrpcNodeBAddress configured.");
         }
 
         var sessionId = Guid.NewGuid().ToString("N");
@@ -104,7 +114,10 @@ public class DebugStreamService
             sessionId,
             commActor,
             onEventWrapper,
-            onTerminatedWrapper);
+            onTerminatedWrapper,
+            _grpcClientFactory,
+            grpcNodeAAddress,
+            grpcNodeBAddress);
 
         var bridgeActor = system.ActorOf(props, $"debug-stream-{sessionId}");