- Added support for fetching and parsing external ICS calendars, allowing events to be displayed on the duty grid.
- Introduced a new API endpoint `/api/calendar-events` to retrieve calendar events within a specified date range.
- Updated configuration to include `EXTERNAL_CALENDAR_ICS_URL` for specifying the ICS calendar URL.
- Enhanced the web application to visually indicate days with events and provide event summaries on hover.
- Improved documentation in the README to include details about the new calendar integration and configuration options.
- Updated tests to cover the new calendar functionality and ensure proper integration.
- Added `__all__` declaration in `db/__init__.py` for better module export management.
- Simplified command text formatting in `handlers/commands.py` for improved readability.
- Refactored error handler function signature in `handlers/errors.py` for better code style.
- Introduced comprehensive tests for API duties and Telegram authentication in new test files.
