Final step of removing inventory quantity tracking - see
docs/superpowers/specs/2026-08-01-remove-inventory-quantity-tracking-design.md.
Destructive to any existing on-hand/transaction data; confirmed
acceptable since nothing read it automatically.
Introduce new data model that separates stock catalog (StockItem) from
supplier-specific pricing/catalog info (SupplierOffering). StockItem
represents a Material+Length combination, while SupplierOffering links
suppliers to stock items with part numbers, descriptions, and pricing.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>