feat(docs): add documentation site and demo features

- Introduced a new documentation site for Cursor BYOK using Next.js and Fumadocs.
- Added a product demo page with a corresponding Vite configuration.
- Implemented a demo API to simulate LLM calls and responses.
- Enhanced the Makefile to include new build and development commands for the documentation.
- Updated package.json scripts for building and running the documentation site.
- Created various components and layouts for the documentation structure, including blog and user documentation sections.
- Added styling for the new components and layouts to ensure a cohesive design.
- Included a README and other necessary files for local development and deployment.

apps/docs/lib/layout.shared.tsx

@@ -0,0 +1,31 @@
+import { zhCN } from '@fumadocs/language/zh-cn';
+import { defineTranslations } from 'fumadocs-core/i18n';
+import type { BaseLayoutProps } from 'fumadocs-ui/layouts/shared';
+import { uiTranslations } from 'fumadocs-ui/i18n';
+import { appName, gitConfig, releaseUrl } from './shared';
+
+export const translations = defineTranslations().extend(uiTranslations()).preset(zhCN());
+
+export function baseOptions(): BaseLayoutProps {
+  return {
+    nav: {
+      title: appName,
+    },
+    links: [
+      {
+        text: '文档',
+        url: '/docs',
+      },
+      {
+        text: '开发者博客',
+        url: '/blog',
+      },
+      {
+        text: '下载',
+        url: releaseUrl,
+        external: true,
+      },
+    ],
+    githubUrl: `https://github.com/${gitConfig.user}/${gitConfig.repo}`,
+  };
+}