feat(products): include ownerId in product creation and enforce its requirement

backend/src/products/products.controller.ts

@@ -128,8 +128,8 @@ export class ProductsController {
 
   @Roles('admin')
   @Post()
-  create(@Body() body: CreateProductDto) {
-    return this.productsService.create(body);
+  create(@Body() body: CreateProductDto, @Request() req: { user: { id: number } }) {
+    return this.productsService.create(body, req.user.id);
   }
 
   // Tillgänglig för alla inloggade användare — req.user.id injiceras av JWT-guard