fix(workflows): export workflowFileStem from workflow-normalize

Restore the missing export so workflow duplication resolves YAML stems
without a broken import from workflow-duplicate.js.

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/server/workflow-normalize.js

@@ -42,6 +42,11 @@ export function workflowIdFromFile(file) {
   return String(file).replace(/\.ya?ml$/i, "");
 }
 
+/** @param {string} file */
+export function workflowFileStem(file) {
+  return workflowIdFromFile(file);
+}
+
 /**
  * New on-disk workflow filename: `{uuid}.yaml`.
  * @param {string} [uuid]