Fix SSE route dependency and align architecture docs

backend/app/config/__init__.py

@@ -1,5 +1,7 @@
-"""配置模块"""
+"""Initialize the app.config package."""
 
 from .settings import Settings, get_settings, settings
+# Keep package boundaries explicit so backend imports stay predictable.
+
 
 __all__ = ["Settings", "get_settings", "settings"]