feat(docs): migrate documentation to Next.js with Fumadocs

This commit migrates the documentation site from Astro to Next.js, leveraging Fumadocs for enhanced functionality and maintainability. The migration includes:
- New Next.js configuration and setup
- Integration of Fumadocs for documentation rendering
- Addition of new documentation assets and images
- Removal of Astro-related files and configurations

The migration aims to improve the documentation site's performance, scalability, and developer experience.

apps/docs/next.config.mjs

@@ -0,0 +1,10 @@
+import { createMDX } from 'fumadocs-mdx/next';
+
+const withMDX = createMDX();
+
+/** @type {import('next').NextConfig} */
+const config = {
+  reactStrictMode: true,
+};
+
+export default withMDX(config);