switch to dataclass, cleanup

app/__init__.py

@@ -1,3 +1,4 @@
+from typing import Optional
 from flask import Flask
 from flask_socketio import SocketIO
 from flask_login import LoginManager
@@ -8,7 +9,7 @@ sIO = SocketIO()
 login_manager = LoginManager()
 
 @login_manager.user_loader
-def load_user(user_id):
+def load_user(user_id: int | str) -> Optional["User"]:
     return User.get(user_id)
 
 def create_app():