F25 (part 2): Sales lines sell products — unit factor snapshots, quantity_base, grade-mapped allocation #99

Spec §10.5 + §9.7 conversion rules. Second half of the Phase 1.1 product-catalog item; builds on the part-1 catalog (#97, PR #98).

Scope

Domain / persistence:

• SalesOrderItem gains: ProductId, ProductTypeSnapshot (spec §10.5), Unit, BaseUnitFactor (eggs-per-unit snapshotted at line creation — §9.7: a later carton/case redefinition must never reinterpret existing orders), QuantityBase (always individual eggs: quantity × factor). Quantity becomes the unit count.
• Data migration: for each egg grade referenced by existing order items, auto-create a product (grade name, unit Egg, mapped to that grade) if none maps to it yet; backfill existing lines with that product, Unit=Egg, BaseUnitFactor=1, QuantityBase=Quantity. Frozen history — no money changes.

Behavior:

• Add-item takes productId + quantity + unit (defaults to the product's DefaultUnit). Factor resolves from the account's active EggUnitConversion row at line creation and is snapshotted; missing/inactive conversion → 422.
• Product must be active and an egg product; allocation reserves QuantityBase eggs FIFO from lots of the product's mapped grade (mapping resolved at line creation — later re-pointing never rewrites existing lines).
• Unit price defaults from the product's default price (per selling unit) when the request omits it; stock/overselling guard runs on QuantityBase.
• Confirm/void/allocation release logic unchanged otherwise; version race tests per AGENTS.md.

SPA (SalesPage): line entry switches from grade picker to product picker (active products) + unit + quantity; shows resolved eggs-per-unit and line total; price prefilled from the product default, editable.

Sync: CSV export sales-order-items dataset gains the new columns; GLOSSARY (Product line, quantity_base) + Help (Customers & sales section) + Help TOC; audit filter untouched (no new actions).

Tests

• Line snapshots: carton=12 at sale, redefine carton=30, old line keeps factor 12 / new line gets 30
• quantity_base math + FIFO allocation from the mapped grade's lots; overselling guard on eggs
• Product inactive / non-mapped / missing conversion → 422
• Migration backfill: pre-existing grade-lines get auto-created products, factor 1, unchanged totals
• Grade re-point after sale: old lines keep the original allocation
• Worker can still record/confirm orders (production-side open); race tests