chore: apply ruff auto-fixes and remove dead AST scripts

tests/test_phase6_engine.py

@@ -1,8 +1,5 @@
 import pytest
 from unittest.mock import MagicMock, patch, AsyncMock
-import asyncio
-import json
-import multi_agent_conductor
 from multi_agent_conductor import ConductorEngine, run_worker_lifecycle
 from models import Ticket, Track, WorkerContext