purchasability-sync-completion changes
Deferred live verification for ladder-tier-append and
multi-price-support to maintainer; stack left running. Validated
ladder-tier-append with openspec --strict. Closed purchasability
checklist issue and marked milestone 10c Done. Archived specs into
archive directory and created db-error-presentation spec. Updated
plan-ladder-management and price-management specs with tier append,
reorder, removal, and price default behavior.
