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/lmxfakeproxy/Dockerfile

@@ -1,4 +1,5 @@
-FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
+# Build stage forced to amd64: Grpc.Tools protoc crashes on linux/arm64 (Apple Silicon)
+FROM --platform=linux/amd64 mcr.microsoft.com/dotnet/sdk:10.0 AS build
 WORKDIR /src
 COPY LmxFakeProxy.csproj .
 RUN dotnet restore