Toolbar: implement undo/redo

https://konvajs.org/docs/react/Undo-Redo.html
https://konvajs.org/docs/data_and_serialization/Best_Practices.html

Start by reading the linked Konva Undo-Redo and Best Practices documentation, then locate the toolbar entry point in the TypeScript application. Determine how editor changes are tracked and how toolbar actions should expose undo and redo. Done means the toolbar provides working undo and redo behavior for the editor.

Written by the indexing model from the issue text.