feat: add configurable logging level for backend and Mini App

- Introduced a new `LOG_LEVEL` configuration option in the `.env.example` file to allow users to set the logging level (DEBUG, INFO, WARNING, ERROR).
- Updated the `Settings` class to include the `log_level` attribute, normalizing its value to ensure valid logging levels are used.
- Modified the logging setup in `run.py` to utilize the configured log level, enhancing flexibility in log management.
- Enhanced the Mini App to include the logging level in the JavaScript configuration, allowing for consistent logging behavior across the application.
- Added a new `logger.js` module for frontend logging, implementing level-based filtering and console delegation.
- Included unit tests for the new logger functionality to ensure proper behavior and level handling.

duty_teller/api/dependencies.py

@@ -20,6 +20,7 @@ from duty_teller.utils.dates import DateRangeValidationError, validate_date_rang
 
 log = logging.getLogger(__name__)
 
+
 def _lang_from_accept_language(header: str | None) -> str:
     """Return the application language: always config.DEFAULT_LANGUAGE.