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

infra/opcua/nodes.json

@@ -133,6 +133,43 @@
           "Description": "Valve command (0=Close, 1=Open, 2=Stop)"
         }
       ]
+    },
+    {
+      "Folder": "JoeAppEngine",
+      "NodeList": [
+        {
+          "NodeId": "JoeAppEngine.BTCS",
+          "Name": "BTCS",
+          "DataType": "String",
+          "ValueRank": -1,
+          "AccessLevel": "CurrentReadOrWrite",
+          "Description": "BTCS string value"
+        },
+        {
+          "NodeId": "JoeAppEngine.AlarmCntsBySeverity",
+          "Name": "AlarmCntsBySeverity",
+          "DataType": "Int32",
+          "ValueRank": 1,
+          "ArrayDimensions": [13],
+          "AccessLevel": "CurrentReadOrWrite",
+          "Description": "13-element alarm counts by severity level"
+        }
+      ],
+      "FolderList": [
+        {
+          "Folder": "Scheduler",
+          "NodeList": [
+            {
+              "NodeId": "JoeAppEngine.Scheduler.ScanTime",
+              "Name": "ScanTime",
+              "DataType": "DateTime",
+              "ValueRank": -1,
+              "AccessLevel": "CurrentReadOrWrite",
+              "Description": "Current scan time (updates every second)"
+            }
+          ]
+        }
+      ]
     }
   ]
 }