Make subcategory optional, source category picker from real tenant data

Matches the backend: subcategory is no longer a required field in the
import modal (defaults to none/0 instead of blocking submission), and
the Category dropdown now comes from GET gettenantcategories (what
this tenant's own products actually use) instead of the global
categories list, which was missing categoryid 2 despite it being the
category tenant 1135 actually needs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/services/catalogueApi.ts

@@ -122,3 +122,18 @@ export async function getProductSubcategories(tenantid: number, categoryid?: num
   const { items } = await apiGet<{ subcategoryid: number; subcategoryname: string }>(url);
   return items;
 }
+
+export interface TenantCategory {
+  categoryid: number;
+  categoryname: string;
+}
+
+// Categories this tenant's own products actually use — not the global
+// productcategories list, which is missing categoryids that are nonetheless
+// in real use (e.g. categoryid 2), which would make the picker unusable.
+export async function getTenantCategories(tenantid: number) {
+  const url = new URL(`${API_BASE}/products/gettenantcategories`);
+  url.searchParams.set("tenantid", String(tenantid));
+  const { items } = await apiGet<TenantCategory>(url);
+  return items;
+}