feat: add article summary post-processing flow

src/summary_mcp/workflows/freshrss_pipeline.py

@@ -2,7 +2,9 @@ from __future__ import annotations
 
 import json
 import os
-from datetime import UTC, date, datetime
+from datetime import date, datetime, timezone
+
+UTC = timezone.utc
 from pathlib import Path
 from typing import Any