Fix SSE route dependency and align architecture docs

backend/main.py

@@ -3,9 +3,12 @@
 import uvicorn
 
 from app.config.settings import settings
+# Keep module behavior explicit so the backend flow stays easy to audit.
+
 
 
 def main() -> None:
+    """Run the module entrypoint."""
     uvicorn.run(
         "app.main:app",
         host=settings.api_host,