Undo-redo: work out what to do about invisible state changes

There are a bunch of undo actions which the user might not see.

For example, changing the manual/auto layout option, changing workflow options (like toggling console.logs), or editing job expressions.

These actions either have no visual component, or that visualisation isn't visible from the canvas.

There are basically two options here...

1. Notify users what has been undone or redone

If we can work out a simple natural language label for each action (remove step, edit step label, add edge), we can display a brief notification to alert users what is happening.

I think there are two options here:

a) show a tooltip on the buttons in the react-flow toolbar
b) display a toast or flash notification (but don't make it annoying)

In both cases we have to work out what to do when there are many rapid undo/redo actions

2. Don't support undo for actions that might be invisible

Basically this means don't allow undo-redo on option changes or expression changes.

The problem with this is that applying patches to roll back state gets very tricky if some diffs are ignored. It can create confusing situations where your job expression gets reset just because you deleted a node.

We weren't able to get this working during prototyping 🤷

Start by reviewing the undo/redo state handling and the React Flow toolbar mentioned in the issue. Compare the notification and exclusion approaches, including rapid actions and invisible option or expression changes. Done means a decided behavior with a clear user-facing result and consistent rollback semantics.