Refactor documentation structure and dependencies for migration to Fumadocs

- Updated `.gitignore` to include new build and generated content directories.
- Removed outdated Mintlify configuration files and documentation.
- Introduced new `MIGRATION.md` to outline the transition from Mintlify to Fumadocs.
- Added `mdx-components.tsx` for MDX component configuration and compatibility.
- Updated `package.json` and `next.config.mjs` for new dependencies and Next.js configuration.
- Created `source.config.ts` for content source configuration.
- Added OpenAPI specification in `openapi.json` for API documentation.
- Removed legacy files and adjusted project structure to align with Fumadocs conventions.

docs/app/og/docs/[...slug]/route.tsx

@@ -0,0 +1,36 @@
+import { getPageImage, source } from '@/lib/source';
+import { notFound } from 'next/navigation';
+import { ImageResponse } from 'next/og';
+import { generate as DefaultImage } from 'fumadocs-ui/og';
+
+export const revalidate = false;
+
+export async function GET(
+  _req: Request,
+  { params }: RouteContext<'/og/docs/[...slug]'>,
+) {
+  const { slug } = await params;
+  const page = source.getPage(slug.slice(0, -1));
+  if (!page) notFound();
+
+  return new ImageResponse(
+    (
+      <DefaultImage
+        title={page.data.title}
+        description={page.data.description}
+        site="My App"
+      />
+    ),
+    {
+      width: 1200,
+      height: 630,
+    },
+  );
+}
+
+export function generateStaticParams() {
+  return source.getPages().map((page) => ({
+    lang: page.locale,
+    slug: getPageImage(page).segments,
+  }));
+}