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.InboundAPI/RouteHelper.cs

@@ -179,8 +179,14 @@ public class RouteTarget
         var siteId = await ResolveSiteAsync(token);
         var correlationId = Guid.NewGuid().ToString();
 
+        // Audit Log #23 (ParentExecutionId): mirrors the Call path — stamp the
+        // spawning inbound request's ExecutionId so future site-side audit
+        // emission for routed reads can record this read's parent. Symmetric
+        // with RouteToCallRequest so script authors get the same correlation
+        // across Call / GetAttributes / SetAttributes.
         var request = new RouteToGetAttributesRequest(
-            correlationId, _instanceCode, attributeNames.ToList(), DateTimeOffset.UtcNow);
+            correlationId, _instanceCode, attributeNames.ToList(), DateTimeOffset.UtcNow,
+            _parentExecutionId);
 
         var response = await _instanceRouter.RouteToGetAttributesAsync(siteId, request, token);
 
@@ -222,8 +228,14 @@ public class RouteTarget
         var siteId = await ResolveSiteAsync(token);
         var correlationId = Guid.NewGuid().ToString();
 
+        // Audit Log #23 (ParentExecutionId): mirrors the Call path — stamp the
+        // spawning inbound request's ExecutionId so future site-side audit
+        // emission for routed writes can record this write's parent. Symmetric
+        // with RouteToCallRequest so script authors get the same correlation
+        // across Call / GetAttributes / SetAttributes.
         var request = new RouteToSetAttributesRequest(
-            correlationId, _instanceCode, attributeValues, DateTimeOffset.UtcNow);
+            correlationId, _instanceCode, attributeValues, DateTimeOffset.UtcNow,
+            _parentExecutionId);
 
         var response = await _instanceRouter.RouteToSetAttributesAsync(siteId, request, token);