Add documents site (#1767)

* feat: add docs site

- Implemented dynamic routing for MDX documentation pages with language support.
- Created layout components for documentation with a header and footer.
- Added metadata for various documentation sections in English and Chinese.
- Developed initial content for the DeerFlow App and Harness documentation.
- Introduced i18n hooks and translations for English and Chinese languages.
- Enhanced header component to include navigation links for documentation and blog.
- Established a structure for tutorials and reference materials.
- Created a new translations file to manage locale-specific strings.

* feat: enhance documentation structure and content for application and harness sections

* feat: update .gitignore to include .playwright-mcp and remove obsolete Playwright YAML file

* fix(docs): correct punctuation and formatting in documentation files

* feat(docs): remove outdated index.mdx file from documentation

* fix(docs): update documentation links and improve Chinese description in index.mdx

* fix(docs): update title in Chinese for meta information in _meta.ts

frontend/next.config.js

@@ -10,9 +10,16 @@ function getInternalServiceURL(envKey, fallbackURL) {
     ? configured.replace(/\/+$/, "")
     : fallbackURL;
 }
+import nextra from "nextra";
+
+const withNextra = nextra({});
 
 /** @type {import("next").NextConfig} */
 const config = {
+  i18n: {
+    locales: ["en", "zh"],
+    defaultLocale: "en",
+  },
   devIndicators: false,
   async rewrites() {
     const rewrites = [];
@@ -51,4 +58,4 @@ const config = {
   },
 };
 
-export default config;
+export default withNextra(config);