Introduce a full-featured workflow automation system: add WorkflowEngine service to execute workflows, background scheduler to trigger cron workflows, and croniter dependency. Extend Workflow model with automation fields (is_active, trigger_type, trigger_config, last_run_at, last_status) and add WorkflowExecution and WorkflowLog models. Add API endpoints to start executions, list executions, fetch execution details and logs, and persist execution records/logs. Implement frontend components for workflow nodes, config panels, and an execution history UI (multiple new React components) and wire minor builder UI imports. Note: database migrations are required to add new columns and tables.