Add backend and frontend skeleton

app/backend/features/auth/router.py

@@ -0,0 +1,11 @@
+"""Authentication router placeholder."""
+
+from fastapi import APIRouter
+
+router = APIRouter(prefix="/auth", tags=["auth"])
+
+
+@router.get("/noop", include_in_schema=False)
+def auth_not_implemented() -> dict:
+    """Placeholder endpoint to keep router wired."""
+    return {"status": "not_implemented"}