fix(manifest): check if manifest action enabled before sending

lib/exe/manifest.php

@@ -5,5 +5,10 @@ if (!defined('DOKU_INC')) {
 }
 require_once(DOKU_INC . 'inc/init.php');
 
+if (!actionOK('manifest')) {
+    http_status(404, 'Manifest has been disabled in DokuWiki configuration.');
+    return;
+}
+
 $manifest = new \dokuwiki\Manifest();
 $manifest->sendManifest();