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* feat(docs): remove outdated index.mdx file from documentation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/content/zh/_meta.ts

@@ -0,0 +1,12 @@
+import type { MetaRecord } from "nextra";
+
+const meta: MetaRecord = {
+  index: {
+    title: "概览",
+  },
+  workspace: {
+    type: "page",
+  },
+};
+
+export default meta;

frontend/src/content/zh/index.mdx

@@ -0,0 +1,6 @@
+---
+title: 概览
+description: 了解 DeerFlow，使用 Harness 构建，并部署应用。
+---
+
+# 概览