smartcommit undo

Undo commits created by the latest accepted Smartcommit plan:

smartcommit undo

Behavior:

• Removes only commits created by the most recent accepted smartcommit plan.
• Restores their changes into the working tree.
• Refuses to run if additional commits were created afterward.
• Refuses to run when the working tree has uncommitted changes.

Undo metadata is stored in .git/smartcommit/history.json.