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.Host/Actors/AkkaHostedService.cs

@@ -216,7 +216,8 @@ akka {{
         var storage = _serviceProvider.GetRequiredService<SiteStorageService>();
         var compilationService = _serviceProvider.GetRequiredService<ScriptCompilationService>();
         var sharedScriptLibrary = _serviceProvider.GetRequiredService<SharedScriptLibrary>();
-        var streamManager = _serviceProvider.GetService<SiteStreamManager>();
+        var streamManager = _serviceProvider.GetRequiredService<SiteStreamManager>();
+        streamManager.Initialize(_actorSystem!);
         var siteRuntimeOptionsValue = _serviceProvider.GetService<IOptions<SiteRuntimeOptions>>()?.Value
             ?? new SiteRuntimeOptions();
         var dmLogger = _serviceProvider.GetRequiredService<ILoggerFactory>()
@@ -325,5 +326,9 @@ akka {{
                 "Created ClusterClient to central with {Count} contact point(s) for site {SiteId}",
                 contacts.Count, _nodeOptions.SiteId);
         }
+
+        // Gate gRPC subscriptions until the actor system and SiteStreamManager are initialized
+        var grpcServer = _serviceProvider.GetService<ScadaLink.Communication.Grpc.SiteStreamGrpcServer>();
+        grpcServer?.SetReady(_actorSystem!);
     }
 }

src/ScadaLink.Host/Program.cs

@@ -156,22 +156,40 @@ try
     }
     else if (nodeRole.Equals("Site", StringComparison.OrdinalIgnoreCase))
     {
-        var builder = Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder(args);
-        builder.ConfigureAppConfiguration(config => config.AddConfiguration(configuration));
+        var builder = WebApplication.CreateBuilder(args);
+        builder.Configuration.AddConfiguration(configuration);
 
         // WP-14: Serilog
-        builder.UseSerilog();
+        builder.Host.UseSerilog();
 
         // WP-17: Windows Service support (no-op when not running as a Windows Service)
-        builder.UseWindowsService();
+        builder.Host.UseWindowsService();
 
-        builder.ConfigureServices((context, services) =>
+        // Read GrpcPort from config (NodeOptions already has default 8083)
+        var grpcPort = configuration.GetValue<int>("ScadaLink:Node:GrpcPort", 8083);
+
+        // Configure Kestrel for HTTP/2 only on the gRPC port
+        builder.WebHost.ConfigureKestrel(options =>
         {
-            SiteServiceRegistration.Configure(services, context.Configuration);
+            options.ListenAnyIP(grpcPort, listenOptions =>
+            {
+                listenOptions.Protocols = Microsoft.AspNetCore.Server.Kestrel.Core.HttpProtocols.Http2;
+            });
         });
 
-        var host = builder.Build();
-        await host.RunAsync();
+        // gRPC server registration
+        builder.Services.AddGrpc();
+        builder.Services.AddSingleton<ScadaLink.Communication.Grpc.SiteStreamGrpcServer>();
+
+        // Existing site service registrations
+        SiteServiceRegistration.Configure(builder.Services, builder.Configuration);
+
+        var app = builder.Build();
+
+        // Map gRPC service — resolves the singleton SiteStreamGrpcServer from DI
+        app.MapGrpcService<ScadaLink.Communication.Grpc.SiteStreamGrpcServer>();
+
+        await app.RunAsync();
     }
     else
     {

src/ScadaLink.Host/ScadaLink.Host.csproj

@@ -17,6 +17,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="Grpc.AspNetCore" Version="2.71.0" />
     <PackageReference Include="Microsoft.Extensions.Hosting.WindowsServices" Version="10.0.5" />
     <PackageReference Include="Serilog.AspNetCore" Version="10.0.0" />
     <PackageReference Include="Serilog.Sinks.Console" Version="6.1.1" />