Changeling cleanup and bugfix (#39843)

* fixes and cleanup

* key

Content.Client/Changeling/UI/ChangelingTransformBoundUserInterface.cs

@@ -0,0 +1,35 @@
+using Content.Shared.Changeling.Systems;
+using JetBrains.Annotations;
+using Robust.Client.UserInterface;
+
+namespace Content.Client.Changeling.UI;
+
+[UsedImplicitly]
+public sealed partial class ChangelingTransformBoundUserInterface(EntityUid owner, Enum uiKey) : BoundUserInterface(owner, uiKey)
+{
+    private ChangelingTransformMenu? _window;
+
+    protected override void Open()
+    {
+        base.Open();
+
+        _window = this.CreateWindow<ChangelingTransformMenu>();
+
+        _window.OnIdentitySelect += SendIdentitySelect;
+
+        _window.Update(Owner);
+    }
+
+    public override void Update()
+    {
+        if (_window == null)
+            return;
+
+        _window.Update(Owner);
+    }
+
+    public void SendIdentitySelect(NetEntity identityId)
+    {
+        SendPredictedMessage(new ChangelingTransformIdentitySelectMessage(identityId));
+    }
+}