Transition "-" (remove) button remains greyed out after undoing an animation reset in Transition Animations

Steps to reproduce:

1. Create a new URP project
2. In the Hierarchy, right-click and select UI Toolkit > Standard Elements > Visual Element
3. Select the VisualElement
4. In the Inspector, expand the Transition Animations foldout
5. Modify any property, e.g. "Duration"
6. Observe the "-" button becomes active
7. Click the "-" button (to reset animation)
8. Click Undo (Cmd+Z)
9. Observe the "-" button

Actual results: The "-" button remains greyed out after Undo

Expected results: The "-" button is active again after Undo, matching the restored state

Reproducible with versions: 6000.6.0b1, 6000.7.0a1

Can’t test with versions: 6000.4.12f1, 6000.5.1f1 (uxml editing In Context not available)

Tested on (OS): macOS 26.5

Notes:

• Undo restores the transition values correctly; only the "-" button's enabled state fails to update
• Button becomes active again only if some property is modified again or another animation list item is added