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/services/group_duty_pin_service.py

@@ -1,7 +1,7 @@
 """Group duty pin: current duty message text, next shift end, pin CRUD. All accept session."""
 
 from datetime import datetime, timezone
-from zoneinfo import ZoneInfo
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 from sqlalchemy.orm import Session
 
@@ -32,7 +32,7 @@ def format_duty_message(duty, user, tz_name: str, lang: str = "en") -> str:
         return t(lang, "duty.no_duty")
     try:
         tz = ZoneInfo(tz_name)
-    except Exception:
+    except ZoneInfoNotFoundError:
         tz = ZoneInfo("Europe/Moscow")
         tz_name = "Europe/Moscow"
     start_dt = datetime.fromisoformat(duty.start_at.replace("Z", "+00:00"))