Fix product import defaulting to 1 in stock, allowing orders with zero real inventory

Quick-import buttons hardcoded quantity:1, which the backend writes straight
to the stock ledger as an "in" entry — letting one order go through for a
product that was never actually stocked. Default to 0 instead, and fix a
fallback path that was silently coercing an explicit 0 back to 1 via `|| 1`.

src/components/CatalogueBrowser.tsx

@@ -236,7 +236,7 @@ export default function CatalogueBrowser({ tenantid, locationid, onClose }: Cata
                                   catalogueid: p.id,
                                   categoryid: validCategory,
                                   subcategoryid: 0,
-                                  quantity: 1,
+                                  quantity: 0,
                                   stocktype: "in",
                                   // Draft: lands in the Admin Catalogue only. It only becomes
                                   // visible to store users once the admin explicitly publishes

src/components/ImportProductModal.tsx

@@ -143,7 +143,7 @@ export default function ImportProductModal({
                     catalogueid: product.id,
                     categoryid: validCategory,
                     subcategoryid: 0,
-                    quantity: 1,
+                    quantity: 0,
                     stocktype: "in",
                     status: "Draft",
                     retailprice: 0,

src/services/catalogueApi.ts

@@ -103,7 +103,7 @@ async function fallbackCreateProductLocation(items: ImportCatalogueProductReques
     tenantid: item.tenantid,
     locationid: item.locationid,
     productid: item.catalogueid,
-    quantity: item.quantity || 1,
+    quantity: item.quantity ?? 0,
     stocktype: item.stocktype || "in",
     status: item.status || "Active",
     retailprice: item.retailprice || 0,