refactor: streamline configuration loading and enhance admin checks

- Refactored the configuration loading in `config.py` to utilize a single source of truth through the `Settings` class, improving maintainability and clarity.
- Introduced the `is_admin_for_telegram_user` function in `repository.py` to centralize admin checks based on usernames and phone numbers.
- Updated command handlers to use the new admin check function, ensuring consistent access control across the application.
- Enhanced error handling in the `error_handler` to log exceptions when sending error replies to users, improving debugging capabilities.
- Improved the handling of user phone updates in `repository.py` to ensure proper normalization and validation of phone numbers.

duty_teller/run.py

@@ -62,6 +62,7 @@ def _run_uvicorn(web_app, port: int) -> None:
 def main() -> None:
     """Build the bot and FastAPI, start uvicorn in a thread, run polling."""
     require_bot_token()
+    # Optional: set bot menu button to open the Miniapp. Uncomment to enable:
     # _set_default_menu_button_webapp()
     app = (
         ApplicationBuilder()