Covers consignment lifecycle, settlement workflow, POS integration,
accounting journal entries (commission income vs consignment payable),
reporting, and business rules. Consignment items use account entity
for consignors (not suppliers).
Replace stripe_customer_id on account with account_processor_link
table. Update account_payment_method to use processor enum +
processor_payment_method_id instead of Stripe-specific fields.
Supports multiple simultaneous processors for migration scenarios.
