Fix SSE route dependency and align architecture docs

backend/app/utils/logger.py

@@ -1,9 +1,13 @@
+"""Provide utility helpers for logger."""
+
 import logging
 import sys
+# Keep module behavior explicit so the backend flow stays easy to audit.
+
 
 
 def setup_logging() -> logging.Logger:
-    """配置日志"""
+    """Handle setup logging."""
     logger = logging.getLogger("app")
     logger.setLevel(logging.INFO)