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.CentralUI/Components/Pages/Monitoring/ParkedMessages.razor

@@ -70,9 +70,11 @@
                         <td class="small"><TimestampDisplay Value="@msg.LastAttemptTimestamp" /></td>
                         <td>
                             <button class="btn btn-outline-success btn-sm py-0 px-1 me-1"
-                                    title="Retry message (not yet implemented)">Retry</button>
+                                    @onclick="() => RetryMessage(msg)" disabled="@_actionInProgress"
+                                    title="Retry message (move back to pending)">Retry</button>
                             <button class="btn btn-outline-danger btn-sm py-0 px-1"
-                                    title="Discard message (not yet implemented)">Discard</button>
+                                    @onclick="() => DiscardMessage(msg)" disabled="@_actionInProgress"
+                                    title="Permanently discard message">Discard</button>
                         </td>
                     </tr>
                 }
@@ -102,6 +104,7 @@
     private bool _searching;
     private string? _errorMessage;
 
+    private bool _actionInProgress;
     private ToastNotification _toast = default!;
     private ConfirmDialog _confirmDialog = default!;
 
@@ -150,4 +153,65 @@
         }
         _searching = false;
     }
+
+    private async Task RetryMessage(ParkedMessageEntry msg)
+    {
+        _actionInProgress = true;
+        try
+        {
+            var request = new ParkedMessageRetryRequest(
+                CorrelationId: Guid.NewGuid().ToString("N"),
+                SiteId: _selectedSiteId,
+                MessageId: msg.MessageId,
+                Timestamp: DateTimeOffset.UtcNow);
+            var response = await CommunicationService.RetryParkedMessageAsync(_selectedSiteId, request);
+            if (response.Success)
+            {
+                _toast.ShowSuccess($"Message {msg.MessageId[..Math.Min(12, msg.MessageId.Length)]} queued for retry.");
+                await FetchPage();
+            }
+            else
+            {
+                _toast.ShowError(response.ErrorMessage ?? "Retry failed.");
+            }
+        }
+        catch (Exception ex)
+        {
+            _toast.ShowError($"Retry failed: {ex.Message}");
+        }
+        _actionInProgress = false;
+    }
+
+    private async Task DiscardMessage(ParkedMessageEntry msg)
+    {
+        var confirmed = await _confirmDialog.ShowAsync(
+            $"Permanently discard message {msg.MessageId[..Math.Min(12, msg.MessageId.Length)]}? This cannot be undone.",
+            "Discard Parked Message");
+        if (!confirmed) return;
+
+        _actionInProgress = true;
+        try
+        {
+            var request = new ParkedMessageDiscardRequest(
+                CorrelationId: Guid.NewGuid().ToString("N"),
+                SiteId: _selectedSiteId,
+                MessageId: msg.MessageId,
+                Timestamp: DateTimeOffset.UtcNow);
+            var response = await CommunicationService.DiscardParkedMessageAsync(_selectedSiteId, request);
+            if (response.Success)
+            {
+                _toast.ShowSuccess($"Message {msg.MessageId[..Math.Min(12, msg.MessageId.Length)]} discarded.");
+                await FetchPage();
+            }
+            else
+            {
+                _toast.ShowError(response.ErrorMessage ?? "Discard failed.");
+            }
+        }
+        catch (Exception ex)
+        {
+            _toast.ShowError($"Discard failed: {ex.Message}");
+        }
+        _actionInProgress = false;
+    }
 }