fix(host,deployment-manager,communication): repair cross-module DI regressions from batch 1-2

- DeploymentManager-008: revert IConfiguration overload (violated OptionsTests
  component-convention); Host now binds the ScadaLink:DeploymentManager section
- SiteStreamGrpcServer: make test-only int ctor internal so DI sees one public
  ctor (resolves ambiguous-constructor failure in SiteCompositionRootTests)
- Host site composition-root test config: supply Cluster:SeedNodes for the new
  ClusterOptionsValidator

tests/ScadaLink.Host.Tests/CompositionRootTests.cs

@@ -298,6 +298,9 @@ public class SiteCompositionRootTests : IDisposable
             ["ScadaLink:Node:RemotingPort"] = "0",
             ["ScadaLink:Node:GrpcPort"] = "0",
             ["ScadaLink:Database:SiteDbPath"] = _tempDbPath,
+            // ClusterOptions requires at least one seed node (ClusterOptionsValidator).
+            ["ScadaLink:Cluster:SeedNodes:0"] = "akka.tcp://scadalink@localhost:2551",
+            ["ScadaLink:Cluster:SeedNodes:1"] = "akka.tcp://scadalink@localhost:2552",
         });
 
         // gRPC server registration (mirrors Program.cs site section)