Fix /docs page 404 error by using createMDXSource with files()

Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

Author: Copilot

apps/site/lib/source.ts

@@ -1,28 +1,12 @@
 import { loader } from 'fumadocs-core/source';
-import { docs } from '@/.source';
+import { createMDXSource } from 'fumadocs-mdx';
+import { docs, meta } from '@/.source';
 
-// Map the docs from .source to the format expected by loader
-// Note: docs from .source is wrapped by _runtime.doc(), not a plain array
-const mappedDocs = docs
-  .filter((doc: any) => doc && doc.info && doc.info.path)
-  .map((doc: any) => {
-    let path = doc.info.path.replace(/\.mdx?$/, '');
-    // Convert index.mdx to empty path for root /docs route
-    if (path === 'index') path = '';
-    
-    return {
-      type: 'page' as const,
-      path,
-      data: {
-        ...doc.data,
-        body: doc.data.default,
-      },
-    };
-  });
+const mdxSource = createMDXSource(docs, meta);
 
 export const source = loader({
   baseUrl: '/docs',
   source: {
-    files: mappedDocs,
+    files: mdxSource.files(),
   },
 });