feat(ui): persist retained window layouts

src/AcDream.App/UI/UiElement.cs

@@ -526,6 +526,18 @@ public abstract class UiElement
                 (int)Parent.Height));
     }
 
+    /// <summary>
+    /// Capture the current mounted rect as the baseline for a compatibility
+    /// anchor policy immediately. Hidden trees do not receive a layout traversal,
+    /// so lazy capture after a persistence resize would use the wrong parent size.
+    /// </summary>
+    internal void CaptureCurrentAnchorBaseline()
+    {
+        if (Parent is null || Anchors == AnchorEdges.None) return;
+        _anchorCaptured = false;
+        ApplyAnchor(Parent.Width, Parent.Height);
+    }
+
     /// <summary>
     /// Rebase each immediate child after a host deliberately changes this element's
     /// design extent. This is used when a production DAT root contains auxiliary