feat(docs): reorganize documentation structure and update navigation links

docs/src/app/llms.txt/route.ts

@@ -0,0 +1,11 @@
+import { source } from '@/lib/source';
+import { llms } from 'fumadocs-core/source';
+import { readFile } from 'node:fs/promises';
+import { join } from 'node:path';
+
+export const revalidate = false;
+
+export async function GET() {
+  const docsIndex = await readFile(join(process.cwd(), 'index.md'), 'utf8');
+  return new Response([docsIndex, llms(source).index()].join('\n\n'));
+}