fix(docs): remove duplicate sitemap plugin to fix build

preset-classic already includes @docusaurus/plugin-sitemap; registering
it again caused 'plugin used 2 times with ID default' error.

Made-with: Cursor

Author: rithulkamesh

website/docusaurus.config.js

@@ -191,9 +191,7 @@ const config = {
     },
   },
 
-  plugins: [
-    require.resolve('@docusaurus/plugin-sitemap'),
-  ],
+  plugins: [],
 };
 
 module.exports = config;