feat: complete gRPC streaming channel — site host, docker config, docs, integration tests

Switch site host to WebApplicationBuilder with Kestrel HTTP/2 gRPC server,
add GrpcPort/keepalive config, wire SiteStreamManager as ISiteStreamSubscriber,
expose gRPC ports in docker-compose, add site seed script, update all 10
requirement docs + CLAUDE.md + README.md for the new dual-transport architecture.

src/ScadaLink.Communication/CommunicationOptions.cs

@@ -33,6 +33,18 @@ public class CommunicationOptions
     /// </summary>
     public List<string> CentralContactPoints { get; set; } = new();
 
+    /// <summary>gRPC keepalive ping interval for streaming connections.</summary>
+    public TimeSpan GrpcKeepAlivePingDelay { get; set; } = TimeSpan.FromSeconds(15);
+
+    /// <summary>gRPC keepalive ping timeout — stream is considered dead if no response within this period.</summary>
+    public TimeSpan GrpcKeepAlivePingTimeout { get; set; } = TimeSpan.FromSeconds(10);
+
+    /// <summary>Maximum lifetime for a single gRPC stream before the server forces re-establishment.</summary>
+    public TimeSpan GrpcMaxStreamLifetime { get; set; } = TimeSpan.FromHours(4);
+
+    /// <summary>Maximum number of concurrent gRPC streaming subscriptions per site node.</summary>
+    public int GrpcMaxConcurrentStreams { get; set; } = 100;
+
     /// <summary>Akka.Remote transport heartbeat interval.</summary>
     public TimeSpan TransportHeartbeatInterval { get; set; } = TimeSpan.FromSeconds(5);
 

src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs

@@ -15,7 +15,7 @@ namespace ScadaLink.Communication.Grpc;
 public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
 {
     private readonly ISiteStreamSubscriber _streamSubscriber;
-    private readonly ActorSystem _actorSystem;
+    private ActorSystem? _actorSystem;
     private readonly ILogger<SiteStreamGrpcServer> _logger;
     private readonly ConcurrentDictionary<string, StreamEntry> _activeStreams = new();
     private readonly int _maxConcurrentStreams;
@@ -24,21 +24,25 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
 
     public SiteStreamGrpcServer(
         ISiteStreamSubscriber streamSubscriber,
-        ActorSystem actorSystem,
         ILogger<SiteStreamGrpcServer> logger,
         int maxConcurrentStreams = 100)
     {
         _streamSubscriber = streamSubscriber;
-        _actorSystem = actorSystem;
         _logger = logger;
         _maxConcurrentStreams = maxConcurrentStreams;
     }
 
     /// <summary>
-    /// Marks the server as ready to accept subscriptions.
-    /// Called after the site runtime is fully initialized.
+    /// Marks the server as ready to accept subscriptions and injects the ActorSystem.
+    /// Called after the site runtime actor system is fully initialized.
+    /// The ActorSystem is set here rather than via the constructor so that
+    /// the gRPC server can be created by DI before the actor system exists.
     /// </summary>
-    public void SetReady() => _ready = true;
+    public void SetReady(ActorSystem actorSystem)
+    {
+        _actorSystem = actorSystem;
+        _ready = true;
+    }
 
     /// <summary>
     /// Number of currently active streaming subscriptions. Exposed for diagnostics.
@@ -72,7 +76,7 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
             new BoundedChannelOptions(1000) { FullMode = BoundedChannelFullMode.DropOldest });
 
         var actorSeq = Interlocked.Increment(ref _actorCounter);
-        var relayActor = _actorSystem.ActorOf(
+        var relayActor = _actorSystem!.ActorOf(
             Props.Create(typeof(Actors.StreamRelayActor), request.CorrelationId, channel.Writer),
             $"stream-relay-{request.CorrelationId}-{actorSeq}");
 
@@ -96,7 +100,7 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
         finally
         {
             _streamSubscriber.RemoveSubscriber(relayActor);
-            _actorSystem.Stop(relayActor);
+            _actorSystem!.Stop(relayActor);
             channel.Writer.TryComplete();
 
             // Only remove our own entry -- a replacement stream may have already taken the slot