Retained stock-source migration evidence

See the repository retirement boundary.

The history mixin and stock-move/picking extensions retain the original field names and stored legacy dates, periods, final proposals, statuses, reasons, explanations, and decision logs. Evidence is immutable through the ORM and is not copied to new records. Current date and period computations no longer depend on migration status. Range refresh preserves archived proposals.

Converters, conversion locks, review mutation actions, historical holds, the proposal-refresh adapter, old upgrade scripts, and obsolete conversion tests have been removed. Since 18.0.2.0.1, the retained scheduled action is inactive and inert, including after upgrade of an existing noupdate job. Source instructions and their convenience manual-period selectors remain active.