chore: add license header for web

web/prettier.config.js

@@ -1,4 +1,7 @@
 /** @type {import('prettier').Config & import('prettier-plugin-tailwindcss').PluginOptions} */
+// Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
+// SPDX-License-Identifier: MIT
+
 export default {
   plugins: ["prettier-plugin-tailwindcss"],
 };