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);