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.

tests/ScadaLink.SiteRuntime.Tests/Streaming/SiteStreamManagerTests.cs

@@ -19,8 +19,8 @@ public class SiteStreamManagerTests : TestKit, IDisposable
     {
         var options = new SiteRuntimeOptions { StreamBufferSize = 100 };
         _streamManager = new SiteStreamManager(
-            Sys, options, NullLogger<SiteStreamManager>.Instance);
-        _streamManager.Initialize();
+            options, NullLogger<SiteStreamManager>.Instance);
+        _streamManager.Initialize(Sys);
     }
 
     void IDisposable.Dispose()