Summary

• skip scratch workspace cleanup when a done parent still has active children
• retry parent cleanup when the last child finishes so deferred scratch dirs are eventually removed
• add regression tests for both the deferred and eventual cleanup paths

Testing

• source .venv/bin/activate && pytest tests/hermes_cli/test_kanban_db.py tests/hermes_cli/test_kanban_scratch_gc.py -x -q -k not\ resolve_hermes_argv