Add unit tests for LoginButton component with comprehensive coverage

backend/api/auth_api.py

@@ -3,9 +3,9 @@ import secrets, jwt
 from datetime import datetime, timedelta, timezone
 from models.user import User
 from flask import Blueprint, request, jsonify, current_app
-from utils.email_instance import email_sender
 from tinydb import Query
 import os
+import utils.email_sender as email_sender
 
 from api.utils import sanitize_email
 from config.paths import get_user_image_dir