Fix NameError: add missing 'g' import in auth.py

The previous commit added g.user_id = ... but forgot to import 'g' from Flask.
This was causing 500 errors on all authenticated API endpoints.

mbetterclient/web_dashboard/auth.py

@@ -7,7 +7,7 @@ import secrets
 import logging
 from datetime import datetime, timedelta
 from typing import Optional, Dict, Any, Tuple, List
-from flask import Flask, request, session, jsonify
+from flask import Flask, request, session, jsonify, g
 from flask_login import UserMixin
 from flask_jwt_extended import create_access_token, decode_token
 import jwt