fix: change database commit to flush in new_user function

- Updated the new_user function in database.py to use db.flush() instead of db.commit() for adding new users. This change ensures that the user object is added to the session without committing the transaction, allowing for better control over database operations.

database.py

@@ -54,7 +54,7 @@ def new_user() -> int:
             user = User()
             user.last_seen = user.created_at = datetime.now(UTC)
             db.add(user)
-            db.commit()
+            db.flush()
             return user.id
     finally:
         db.close()