feat: add JoeAppEngine OPC UA nodes, fix DCL auto-reconnect and quality push

- Add JoeAppEngine folder to OPC UA nodes.json (BTCS, AlarmCntsBySeverity, Scheduler/ScanTime)
- Fix DataConnectionActor: capture Self in PreStart for use from non-actor threads,
  preventing Self.Tell failure in Disconnected event handler
- Implement InstanceActor.HandleConnectionQualityChanged to mark attributes Bad on disconnect
- Fix LmxFakeProxy TagMapper to serialize arrays as JSON instead of "System.Int32[]"
- Allow DataType and DataSourceReference updates in TemplateService.UpdateAttributeAsync
- Update test_infra_opcua.md with JoeAppEngine documentation

src/ScadaLink.HealthMonitoring/SiteHealthCollector.cs

@@ -114,6 +114,9 @@ public class SiteHealthCollector : ISiteHealthCollector
         // Snapshot current S&F buffer depths
         var sfBufferDepths = new Dictionary<string, int>(_sfBufferDepths);
 
+        // Determine node role from active/standby state
+        var nodeRole = _isActiveNode ? "Active" : "Standby";
+
         return new SiteHealthReport(
             SiteId: siteId,
             SequenceNumber: 0, // Caller (HealthReportSender) assigns the sequence number
@@ -126,6 +129,7 @@ public class SiteHealthCollector : ISiteHealthCollector
             DeadLetterCount: deadLetters,
             DeployedInstanceCount: _deployedInstanceCount,
             EnabledInstanceCount: _enabledInstanceCount,
-            DisabledInstanceCount: _disabledInstanceCount);
+            DisabledInstanceCount: _disabledInstanceCount,
+            NodeRole: nodeRole);
     }
 }