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.Commons/Interfaces/Protocol/IDataConnection.cs

@@ -22,4 +22,11 @@ public interface IDataConnection : IAsyncDisposable
     Task<IReadOnlyDictionary<string, WriteResult>> WriteBatchAsync(IDictionary<string, object?> values, CancellationToken cancellationToken = default);
     Task<bool> WriteBatchAndWaitAsync(IDictionary<string, object?> values, string flagPath, object? flagValue, string responsePath, object? responseValue, TimeSpan timeout, CancellationToken cancellationToken = default);
     ConnectionHealth Status { get; }
+
+    /// <summary>
+    /// Raised when the adapter detects an unexpected connection loss (e.g., gRPC stream error,
+    /// network timeout). The DataConnectionActor listens for this to trigger reconnection
+    /// and push bad quality to all subscribed tags.
+    /// </summary>
+    event Action? Disconnected;
 }