Undo the most recent file operation by restoring to the previous checkpoint.

This is a quick way to revert the last change. It restores all files to their state at the second-most-recent checkpoint (since the most recent checkpoint captures the current state).

Parameters:
- confirm: Set to false to preview what would be undone without executing (default: true)

Usage:
- Quick undo: undo
- Preview first: undo confirm=false

If you need to undo multiple operations or restore to a specific point, use checkpoint_list and checkpoint_restore instead.

After undo, you can "redo" by using checkpoint_restore with the previous commit hash (shown in the output).