fix: Revert markdown config to use deprecated but working option

The new markdown.onBrokenMarkdownLinks path is not yet supported in
Docusaurus 3.9.2. Revert to the deprecated but working config option.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: gouravjshah

docusaurus.config.js

@@ -17,10 +17,7 @@ const config = {
   trailingSlash: false,
 
   onBrokenLinks: 'throw',
-
-  markdown: {
-    onBrokenMarkdownLinks: 'warn',
-  },
+  onBrokenMarkdownLinks: 'warn',
 
   i18n: {
     defaultLocale: 'en',