app/constants: add zip file extension and mime type

src/app/constants.ts

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: MIT
-// Copyright (c) 2021-2022 The Pybricks Authors
+// Copyright (c) 2021-2023 The Pybricks Authors
 import docsPackage from '@pybricks/ide-docs/package.json';
 
 // Definitions for compile-time UI settings.
@@ -81,3 +81,9 @@ export const docsPathPrefix = `static/docs/v${docsPackage.version}/`;
 
 /** The index page of the docs. */
 export const docsDefaultPage = `${docsPathPrefix}index.html`;
+
+/** The ZIP file extension ('.zip') */
+export const zipFileExtension = '.zip';
+
+/** The ZIP file MIME type ('application/zip') */
+export const zipFileMimeType = 'application/zip';