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/index.html

@@ -58,6 +58,7 @@
         "./js/dutyList.js": "./js/dutyList.js?v=2",
         "./js/hints.js": "./js/hints.js?v=2",
         "./js/i18n.js": "./js/i18n.js?v=3",
+        "./js/logger.js": "./js/logger.js?v=1",
         "./js/theme.js": "./js/theme.js?v=2",
         "./js/ui.js": "./js/ui.js?v=2",
         "./js/utils.js": "./js/utils.js?v=2"