Fixes: 1) Remove unused `get_avatar_url` method in `UserSerializer`.
Extra: 1) Reorganize imports in serializers and middleware for clarity; 2) General code cleanup in `UserSerializer`.
Fixes: 1) Updated email templates to use `STOREFRONT_DOMAIN` instead of `FRONTEND_DOMAIN`; 2) Added a missing import for `settings` in emailing utilities;
Extra: 1) Removed unused configuration keys `FRONTEND_DOMAIN` and `BASE_DOMAIN`; 2) Cleaned up obsolete imports and formatting in serializers; 3) Adjusted environment file generation scripts to use `STOREFRONT_DOMAIN`.
