refactor: standardize runtime annotation types across multiple files

backend/scripts/export_openapi.py

@@ -9,11 +9,11 @@ from pathlib import Path
 BACKEND_ROOT = Path(__file__).resolve().parents[1]
 sys.path.insert(0, str(BACKEND_ROOT))
 
-from app.main import app  # noqa: E402
-
 
 def main() -> None:
     """Generate `openapi.json` from the FastAPI app definition."""
+    from app.main import app
+
     # Importing the FastAPI app does not run lifespan hooks,
     # so this does not require a DB.
     out_path = BACKEND_ROOT / "openapi.json"