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.

tests/test_api_dependencies.py

@@ -17,7 +17,9 @@ class TestLangFromAcceptLanguage:
         assert deps._lang_from_accept_language(None) == config.DEFAULT_LANGUAGE
         assert deps._lang_from_accept_language("") == config.DEFAULT_LANGUAGE
         assert deps._lang_from_accept_language("   ") == config.DEFAULT_LANGUAGE
-        assert deps._lang_from_accept_language("ru-RU,ru;q=0.9") == config.DEFAULT_LANGUAGE
+        assert (
+            deps._lang_from_accept_language("ru-RU,ru;q=0.9") == config.DEFAULT_LANGUAGE
+        )
         assert deps._lang_from_accept_language("en-US") == config.DEFAULT_LANGUAGE
         assert deps._lang_from_accept_language("zz") == config.DEFAULT_LANGUAGE
         assert deps._lang_from_accept_language("x") == config.DEFAULT_LANGUAGE