Clarify demo trash icon / undo

[frostburn]

Is your feature request related to a problem? Please describe.
In demo mode. It's not immediately obvious what the trash icon (🗑) does.
The prompt makes it sound like the whole branch is going to be deleted all the way to the where it splits out from a parent node.

Describe the solution you'd like

1. When navigation is at the end of a branch the icon changes to an undo icon (↺ or ⎌) and there's no confirmation prompt when clicked. (Possibly only do this when the current node is the latest node created so that "undo" actually undoes the last action.)
2. When multiple nodes are affected there's a confirmation prompt that cleary indicates that only the current node and subsequent nodes are affected.

Describe alternatives you've considered
When relaying games I had to go back, make a new move branch and only then delete the misclick because I was afraid the whole mainline was going to be deleted otherwise.

Additional context
Turns out I was just a scaredy-cat 🙀. The trash icon works reasonably.