chore(sample): add comments for _app and _document

apps/sample/src/pages/_app.tsx

@@ -1,3 +1,16 @@
+/**
+ * _app.tsx
+ *
+ * This is a special Next.js file used to wrap the entire application and provide a common
+ * layout or functionality across all pages. It allows you to maintain state, apply global
+ * styles, and handle other aspects that should persist across different pages.
+ *
+ * The `App` component in this file is initialized once for the entire application and is
+ * used to customize the rendering of pages. For more information, refer to the Next.js
+ * documentation on customizing the App component:
+ * https://nextjs.org/docs/advanced-features/custom-app
+ */
+
 import { CustomThemeProvider } from "@/providers/theme";
 import { GlobalStyle } from "@/styles/globalstyles";
 import type { AppProps } from "next/app";

apps/sample/src/pages/_document.tsx

@@ -1,3 +1,16 @@
+/**
+ * _document.tsx
+ *
+ * This is a special Next.js file used to create a custom document layout. It allows you
+ * to enhance and optimize the server-side rendering of your application by customizing
+ * the HTML document structure. This file is crucial for implementing global styles, meta
+ * tags, and other layout-related configurations that should be applied on the server side.
+ *
+ * Keep in mind that changes made in this file affect the entire application's HTML structure,
+ * so use it judiciously. For more information, refer to the Next.js documentation on customizing
+ * the document: https://nextjs.org/docs/advanced-features/custom-document
+ */
+
 import type { DocumentContext, DocumentInitialProps } from "next/document";
 import Document from "next/document";
 import { ServerStyleSheet } from "styled-components";