Create Workflow via Webhook in n8n

1. **Validation Error**: Sets a JSON response with `success: false` and uses the incoming `$json.message` as the error message when the initial payload validation fails.

2. **API Error**: Sets a JSON response with `success: false`, a fixed `message: "Error creating workflow"`, includes the full error payload (`error: JSON.stringify($json)`), and the HTTP `statusCode` from the failed API request.