feat(commons): carry DataSourceReferenceOverride on ConnectionBinding (additive)

src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/InstanceCommands.cs

@@ -12,8 +12,17 @@ public record MgmtDeleteInstanceCommand(int InstanceId);
 /// <see cref="SetConnectionBindingsCommand"/>. This is a named record (not a
 /// <c>ValueTuple</c>) so it serializes with stable, named JSON properties and can
 /// evolve additively per REQ-COM-5a.
+/// <para>
+/// <c>DataSourceReferenceOverride</c> is an optional per-instance override of
+/// the OPC UA node id (or other protocol address) for the bound attribute.
+/// When non-null it replaces the template's <c>DataSourceReference</c> at
+/// flattening time; when null the template default is used.
+/// </para>
 /// </summary>
-public record ConnectionBinding(string AttributeName, int DataConnectionId);
+public record ConnectionBinding(
+    string AttributeName,
+    int DataConnectionId,
+    string? DataSourceReferenceOverride = null);
 
 public record SetConnectionBindingsCommand(int InstanceId, IReadOnlyList<ConnectionBinding> Bindings);
 public record SetInstanceOverridesCommand(int InstanceId, IReadOnlyDictionary<string, string?> Overrides);