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* feat(docs): remove outdated index.mdx file from documentation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/src/app/[lang]/docs/layout.tsx

@@ -0,0 +1,51 @@
+import type { PageMapItem } from "nextra";
+import { getPageMap } from "nextra/page-map";
+import { Footer, Layout } from "nextra-theme-docs";
+
+import { Header } from "@/components/landing/header";
+import { getLocaleByLang } from "@/core/i18n/locale";
+import "nextra-theme-docs/style.css";
+
+const footer = <Footer>MIT {new Date().getFullYear()} © Nextra.</Footer>;
+
+const i18n = [
+  { locale: "en", name: "English" },
+  { locale: "zh", name: "中文" },
+];
+
+function formatPageRoute(base: string, items: PageMapItem[]): PageMapItem[] {
+  return items.map((item) => {
+    if ("route" in item) {
+      item.route = `${base}${item.route}`;
+    }
+    if ("children" in item && item.children) {
+      item.children = formatPageRoute(base, item.children);
+    }
+    return item;
+  });
+}
+
+export default async function DocLayout({ children, params }) {
+  const { lang } = await params;
+  const locale = getLocaleByLang(lang);
+  const pages = await getPageMap(`/${lang}`);
+
+  return (
+    <Layout
+      navbar={
+        <Header
+          className="relative max-w-full px-10"
+          homeURL="/"
+          locale={locale}
+        />
+      }
+      pageMap={formatPageRoute(`/${lang}/docs`, pages)}
+      docsRepositoryBase="https://github.com/bytedance/deerflow/tree/main/frontend/src/app/content"
+      footer={footer}
+      i18n={i18n}
+      // ... Your additional layout options
+    >
+      {children}
+    </Layout>
+  );
+}