fix(lint): remove trailing whitespace from blank lines in test files

backend/tests/test_auth.py

@@ -37,7 +37,7 @@ def test_login_inactive_user(client, db):
     """Test login with inactive user returns 400."""
     from app.auth import hash_password
     from app.models.user import User
-    
+
     user = User(
         username="inactive",
         hashed_password=hash_password("password"),
@@ -46,7 +46,7 @@ def test_login_inactive_user(client, db):
     )
     db.add(user)
     db.commit()
-    
+
     response = client.post(
         "/api/v1/auth/login",
         data={"username": "inactive", "password": "password"},