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/Messages/Management/DeploymentCommands.cs

@@ -2,3 +2,4 @@ namespace ScadaLink.Commons.Messages.Management;
 
 public record MgmtDeployArtifactsCommand(int? SiteId = null);
 public record QueryDeploymentsCommand(int? InstanceId = null, string? Status = null, int Page = 1, int PageSize = 50);
+public record GetDeploymentDiffCommand(int InstanceId);