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/shared.ts

@@ -0,0 +1,13 @@
+export const appName = 'cursor-byok';
+export const appDescription = 'Cursor 服务端的开源替代';
+export const docsRoute = '/docs';
+export const docsImageRoute = '/og/docs';
+export const docsContentRoute = '/llms.mdx/docs';
+export const repositoryUrl = 'https://github.com/leookun/cursor-byok';
+export const releaseUrl = `${repositoryUrl}/releases/latest`;
+
+export const gitConfig = {
+  user: 'leookun',
+  repo: 'cursor-byok',
+  branch: 'main',
+};