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.

webapp/js/i18n.js

@@ -110,7 +110,7 @@ export const MESSAGES = {
     "contact.back": "Назад",
     "contact.phone": "Телефон",
     "contact.telegram": "Telegram",
-    "current_duty.title": "Текущее дежурство",
+    "current_duty.title": "Сейчас дежурит",
     "current_duty.no_duty": "Сейчас никто не дежурит",
     "current_duty.shift": "Смена",
     "current_duty.remaining": "Осталось: {hours}ч {minutes}мин",