- Introduced a new `normalize_lang` function to standardize language codes across the application, ensuring consistent handling of user language preferences.
- Refactored date handling utilities by adding `parse_utc_iso` and `parse_utc_iso_naive` functions for better parsing of ISO 8601 date strings, enhancing timezone awareness.
- Updated various modules to utilize the new language normalization and date parsing functions, improving code clarity and maintainability.
- Enhanced error handling in date validation to raise specific `DateRangeValidationError` exceptions, providing clearer feedback on validation issues.
- Improved test coverage for date range validation and language normalization functionalities, ensuring robustness and reliability.
- Introduced a new `i18n.js` module for handling translations and language detection, supporting both Russian and English.
- Updated various components to utilize the new translation functions, enhancing user experience by providing localized messages for errors, hints, and UI elements.
- Refactored existing code in `api.js`, `calendar.js`, `dutyList.js`, `hints.js`, and `ui.js` to replace hardcoded strings with translated messages, improving maintainability and accessibility.
- Enhanced the initialization process in `main.js` to set the document language and update UI elements based on the user's language preference.
- Deleted the `app.js` file and migrated its functionality to a modular structure with multiple JavaScript files for better organization and maintainability.
- Updated `index.html` to reference the new `main.js` module, ensuring proper loading of the application.
- Introduced new utility modules for API requests, authentication, calendar handling, and DOM manipulation to enhance code clarity and separation of concerns.
- Enhanced CSS styles for improved layout and theming consistency across the application.
- Added comprehensive comments and documentation to new modules to facilitate future development and understanding.
