fix(ecommerce): sintaxis correcta de +categories en fields de /store/products

+categories sin .* no expande la relacion (Medusa la omite en
silencio del response); +categories.* si trae los sub-campos.
Confirmado en vivo via kubectl exec antes de este commit: demo
con categoria real asignada ahora la trae, legacy sigue en []
(pendiente fix #2, fuera de alcance de este cambio).

workloads/ecommerce/lib/headless/providers/medusa.ts

@@ -528,7 +528,7 @@ async function fetchProducts(
     // region_id.
     region_id: regionId(),
     fields:
-      "+metadata,+images,+tags,+categories,+collection,+variants.inventory_quantity,+variants.calculated_price,+variants.options",
+      "+metadata,+images,+tags,+categories.*,+collection,+variants.inventory_quantity,+variants.calculated_price,+variants.options",
   });
 
   if (filters?.query) {
@@ -559,7 +559,7 @@ export const medusaCatalogProvider: CatalogProvider = {
       // region_id.
       region_id: regionId(),
       fields:
-        "+metadata,+images,+tags,+categories,+collection,+variants.inventory_quantity,+variants.calculated_price,+variants.options",
+        "+metadata,+images,+tags,+categories.*,+collection,+variants.inventory_quantity,+variants.calculated_price,+variants.options",
     });
 
     const response = await medusaFetch<MedusaProductsResponse>(