Revert "Revert purchase order"

This reverts commit 657a201fc0.

internal/transformer/purchase_order_transformer_test.go

@@ -12,15 +12,19 @@ import (
 )
 
 func TestCreatePurchaseOrderRequestToModelAllowsMissingDueDate(t *testing.T) {
+	ingredientID := uuid.New()
+	quantity := 1.0
+	unitID := uuid.New()
+
 	result, err := CreatePurchaseOrderRequestToModel(&contract.CreatePurchaseOrderRequest{
 		VendorID:        uuid.New(),
 		PONumber:        "PO-001",
 		TransactionDate: "2026-05-29",
 		Items: []contract.CreatePurchaseOrderItemRequest{
 			{
-				IngredientID: uuid.New(),
-				Quantity:     1,
-				UnitID:       uuid.New(),
+				IngredientID: &ingredientID,
+				Quantity:     &quantity,
+				UnitID:       &unitID,
 				Amount:       1000,
 			},
 		},