chore(sync): Task 3 review fixes——删未用 import + module docstring 诚实化 + repr(exc) 一致 + 批处理 guard

Co-Authored-By: Claude <noreply@anthropic.com>

yunke-server/tests/test_sync_call_recordings.py

@@ -29,7 +29,6 @@ from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
 from app.db.base import Base
 from app.db.models import PhoneCall, SyncRun
-from app.scraper.media import download_call_recordings
 from app.session.yunke_client import YunkeClient
 from app.storage.object_store import ObjectStore
 from app.sync import orchestrator