Implement group duty pinning and user phone management

- Added functionality to pin duty messages in group chats, including scheduling updates and handling bot add/remove events.
- Introduced a new `GroupDutyPin` model to store pinned message details and a `phone` field in the `User` model for user contact information.
- Implemented commands for users to set or clear their phone numbers in private chats.
- Enhanced the repository with functions to manage group duty pins and user phone data.
- Updated handlers to register new commands and manage duty pin updates effectively.

config.py

@@ -44,6 +44,9 @@ CORS_ORIGINS = (
 # Optional: URL of a public ICS calendar (e.g. holidays). Empty = no external calendar; /api/calendar-events returns [].
 EXTERNAL_CALENDAR_ICS_URL = os.getenv("EXTERNAL_CALENDAR_ICS_URL", "").strip()
 
+# Timezone for displaying duty times in the pinned group message (e.g. Europe/Moscow).
+DUTY_DISPLAY_TZ = os.getenv("DUTY_DISPLAY_TZ", "Europe/Moscow").strip() or "Europe/Moscow"
+
 
 def is_admin(username: str) -> bool:
     """True if the given Telegram username (no @, any case) is in ADMIN_USERNAMES."""