#795 Workflow marked completed prematurely when main task yields for branches

When tools.workflow.execute completes at a fork point to spawn branches, the workflow_run status is set to 'completed' immediately. This is wrong - status should remain 'running' until all branches complete. Location: engine/orchestrator.py lines 610-619 Root cause: The condition 'if task_name != BRANCH_EXECUTION_TASK' marks workflow complete for main task, even when branches are pending. Impact: UI shows workflow as 'completed' while tasks are still running. Status gets corrected later when actual final task completes/fails. Fix: Only mark workflow completed when ALL tasks (main + branches) are done, not just when main task yields.