feat(dcl): extend CreateConnectionCommand with backup config and failover retry count

Update CreateConnectionCommand to carry PrimaryConnectionDetails,
BackupConnectionDetails, and FailoverRetryCount. Update all callers:
DataConnectionManagerActor, DataConnectionActor, DeploymentManagerActor,
FlatteningService, and ConnectionConfig. The actor stores both configs
but continues using primary only — failover logic comes in Task 3.

src/ScadaLink.DataConnectionLayer/Actors/DataConnectionActor.cs

@@ -61,6 +61,9 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
     private int _resolvedTags;
 
     private readonly IDictionary<string, string> _connectionDetails;
+    private readonly IDictionary<string, string> _primaryConfig;
+    private readonly IDictionary<string, string>? _backupConfig;
+    private readonly int _failoverRetryCount;
 
     /// <summary>
     /// Captured Self reference for use from non-actor threads (event handlers, callbacks).
@@ -73,13 +76,18 @@ public class DataConnectionActor : UntypedActor, IWithStash, IWithTimers
         IDataConnection adapter,
         DataConnectionOptions options,
         ISiteHealthCollector healthCollector,
-        IDictionary<string, string>? connectionDetails = null)
+        IDictionary<string, string>? primaryConfig = null,
+        IDictionary<string, string>? backupConfig = null,
+        int failoverRetryCount = 3)
     {
         _connectionName = connectionName;
         _adapter = adapter;
         _options = options;
         _healthCollector = healthCollector;
-        _connectionDetails = connectionDetails ?? new Dictionary<string, string>();
+        _primaryConfig = primaryConfig ?? new Dictionary<string, string>();
+        _backupConfig = backupConfig;
+        _failoverRetryCount = failoverRetryCount;
+        _connectionDetails = _primaryConfig;
     }
 
     protected override void PreStart()

src/ScadaLink.DataConnectionLayer/Actors/DataConnectionManagerActor.cs

@@ -45,10 +45,13 @@ public class DataConnectionManagerActor : ReceiveActor
         }
 
         // WP-34: Factory creates the correct adapter based on protocol type
-        var adapter = _factory.Create(command.ProtocolType, command.ConnectionDetails);
+        var adapter = _factory.Create(command.ProtocolType, command.PrimaryConnectionDetails);
 
         var props = Props.Create(() => new DataConnectionActor(
-            command.ConnectionName, adapter, _options, _healthCollector, command.ConnectionDetails));
+            command.ConnectionName, adapter, _options, _healthCollector,
+            command.PrimaryConnectionDetails,
+            command.BackupConnectionDetails,
+            command.FailoverRetryCount));
 
         // Sanitize name for Akka actor path (replace spaces and invalid chars)
         var actorName = new string(command.ConnectionName