docs+code: close Theme 1 — 24 design-doc / XML-doc drift findings

Doc/XML-comment drift + small adherence fixes across 17 modules. Highlights:
- Host-017: site CoordinatedShutdown ordering — SiteStreamGrpcServer gains
  CancelAllStreams() (refuse new streams, cancel active), wired into
  Program.cs site branch via ApplicationStopping.
- InboundAPI-021: ParentExecutionId now travels on RouteToGet/SetAttributes
  symmetric with RouteToCallRequest; RouteHelper stamps from _parentExecutionId.
- ClusterInfra-012: ClusterOptionsValidator now requires both seed nodes.
- Comm-018: SiteCommunicationActor.HeartbeatMessage.IsActive derived from
  cluster leader check (was hardcoded true).
- DM-020: reconciliation audit row attributes the current user, not prior deployer.
- SEL-019: EventLogPurgeService early-exits on standby via active-node check.
- Plus comment/XML-doc accuracy fixes across AuditLog, ConfigurationDatabase,
  NotificationOutbox, SiteRuntime, SiteCallAudit; doc refreshes for Component-
  Commons / -ManagementService / -CLI / -ExternalSystemGateway / -HealthMonitoring
  / -Transport / -ConfigurationDatabase; CD-023 index-name doc alignment.

11 new regression tests (RouteHelper x4, SiteStreamGrpcServer x2,
ClusterOptionsValidator x1, SiteCommunicationActor x1, DeploymentService x1,
EventLogPurgeService x3). Build clean (0 warnings); InboundAPI/Communication/
Host suites all green. README regenerated: 112 open (was 136).

src/ScadaLink.ConfigurationDatabase/Repositories/DeploymentManagerRepository.cs

@@ -6,11 +6,12 @@ using ScadaLink.Commons.Interfaces.Repositories;
 namespace ScadaLink.ConfigurationDatabase.Repositories;
 
 /// <summary>
-/// EF Core implementation of IDeploymentManagerRepository.
-/// Provides storage/query of deployed configuration snapshots per instance,
-/// current deployment status, and optimistic concurrency on deployment status records.
-///
-/// WP-24: Stub level sufficient for diff/staleness support.
+/// EF Core implementation of <see cref="IDeploymentManagerRepository"/> covering
+/// the deployment pipeline's persistence surface: <c>DeploymentRecord</c> CRUD
+/// (with optimistic concurrency via <c>DeploymentRecord.RowVersion</c>),
+/// <c>SystemArtifactDeploymentRecord</c> CRUD, <c>DeployedConfigSnapshot</c> CRUD,
+/// and a Restrict-FK-aware <see cref="DeleteInstanceAsync"/> that explicitly
+/// clears dependent deployment-record rows before removing an instance.
 /// </summary>
 public class DeploymentManagerRepository : IDeploymentManagerRepository
 {