feat: support JSON import for test cases and add Traditional Chinese locale

JSON import lets users round-trip cases exported via the JSON download
endpoint back into a folder, alongside the existing Excel import path.

frontend/src/middleware.ts

@@ -4,5 +4,5 @@ import { routing } from './i18n/routing';
 export default createMiddleware(routing);
 
 export const config = {
-  matcher: ['/', '/(de|en|pt-BR|zh-CN|ja)/:path*'],
+  matcher: ['/', '/(de|en|pt-BR|zh-CN|zh-TW|ja)/:path*'],
 };