app.workflowManager doesn't exist in the modern Vue-based frontend.
The active workflow is accessed via the Pinia store at
app.extensionManager.workflow.activeWorkflow. Also replaces the
non-existent addEventListener("changeWorkflow") with Pinia's
$onAction watching for "openWorkflow" actions.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>