refactor(settings): one load-change-save update for all settings

readme.md

@@ -134,6 +134,8 @@ layers:
 `user` owns the tables `users` and `user_settings` through the one JPA entity `UserEntity`. `login` and
 `registration` read and write `users` with `JdbcTemplate` (refresh tokens stay JPA). Every query for "a user who
 may log in and is shown to others" uses `shared/account/ActiveUser`.
+A settings change is one `UserRepository.update(userId, change)`: load the user, change the model, write back the
+display name and the settings. A new setting needs no new repository method.
 `profile` and `stats` only read data. They have no entities and use `JdbcTemplate` queries in a `repo` package.
 `version` has only an `api` package: `GET /api/version` answers the commit and build time of the running image.
 `account` (delete and nightly cleanup) sets the flag with `JdbcTemplate` in a `repo` package too, and calls Core