Add products, inventory units, stock receipts, and price history

- product table (catalog definition, no cost column — cost tracked
  per receipt/unit)
- inventory_unit table (serialized items with serial number,
  condition, status)
- stock_receipt table (FIFO cost tracking — records every stock
  receive event with cost_per_unit, supplier, date)
- price_history table (logs every retail price change for margin
  analysis over time)
- product_supplier join table (many-to-many, tracks supplier SKU
  and preferred supplier)
- Full CRUD routes + search (name, SKU, UPC, brand)
- Inventory unit routes nested under products
- Price changes auto-logged on product update
- 33 tests passing

packages/shared/src/schemas/index.ts

@@ -21,10 +21,21 @@ export {
   CategoryUpdateSchema,
   SupplierCreateSchema,
   SupplierUpdateSchema,
+  ItemCondition,
+  UnitStatus,
+  ProductCreateSchema,
+  ProductUpdateSchema,
+  ProductSearchSchema,
+  InventoryUnitCreateSchema,
+  InventoryUnitUpdateSchema,
 } from './inventory.schema.js'
 export type {
   CategoryCreateInput,
   CategoryUpdateInput,
   SupplierCreateInput,
   SupplierUpdateInput,
+  ProductCreateInput,
+  ProductUpdateInput,
+  InventoryUnitCreateInput,
+  InventoryUnitUpdateInput,
 } from './inventory.schema.js'