Cumulative ↔ Monthly Migration Wizard

A one-time, bidirectional wizard moves a branch between cumulative and monthly billing in three steps: Preview → Configure → Execute. Preview is idempotent (run it 100 times, nothing changes); Execute is one-way.

Forward (cumulative → monthly): a positive balance becomes a Migration Invoice; a negative balance becomes a Customer Credit. Cumulative history is retained, not deleted. Always back up before executing.