feat: add team calendar ICS endpoint and related functionality

- Implemented a new API endpoint to generate an ICS calendar for team duty shifts, accessible via a valid token.
- Enhanced the `calendar_link` command to return both personal and team calendar URLs.
- Added a new function to build the team ICS file, ensuring each event includes the duty holder's name in the description.
- Updated tests to cover the new team calendar functionality, including validation for token formats and response content.
- Revised internationalization messages to reflect the new team calendar links.

duty_teller/i18n/messages.py

@@ -15,10 +15,12 @@ MESSAGES: dict[str, dict[str, str]] = {
         "help.pin_duty": "/pin_duty — In a group: pin the duty message (bot needs admin with Pin messages)",
         "calendar_link.private_only": "The /calendar_link command is only available in private chat.",
         "calendar_link.access_denied": "Access denied.",
-        "calendar_link.success": "Your personal calendar URL:\n{url}",
+        "calendar_link.success": (
+            "Personal (your duties only):\n{url_personal}\n\n"
+            "Team (all duties):\n{url_team}"
+        ),
         "calendar_link.help_hint": (
-            "Subscribe to this URL in Google Calendar, Apple Calendar, or Outlook to "
-            "see only your duties."
+            "Subscribe to these URLs in Google Calendar, Apple Calendar, or Outlook."
         ),
         "calendar_link.error": "Could not generate link. Please try again later.",
         "help.import_schedule": "/import_duty_schedule — Import duty schedule (JSON)",
@@ -82,8 +84,13 @@ MESSAGES: dict[str, dict[str, str]] = {
         "help.pin_duty": "/pin_duty — В группе: закрепить сообщение о дежурстве (нужны права админа у бота)",
         "calendar_link.private_only": "Команда /calendar_link доступна только в личке.",
         "calendar_link.access_denied": "Доступ запрещён.",
-        "calendar_link.success": "Ссылка на ваш календарь:\n{url}",
-        "calendar_link.help_hint": "Подпишитесь на эту ссылку в Google Календаре, Календаре Apple или Outlook, чтобы видеть только свои дежурства.",
+        "calendar_link.success": (
+            "Персональный (только ваши дежурства):\n{url_personal}\n\n"
+            "Общий (все дежурства):\n{url_team}"
+        ),
+        "calendar_link.help_hint": (
+            "Подпишитесь на эти ссылки в Google Календаре, Календаре Apple или Outlook."
+        ),
         "calendar_link.error": "Не удалось сформировать ссылку. Попробуйте позже.",
         "help.import_schedule": "/import_duty_schedule — Импорт расписания дежурств (JSON)",
         "help.set_role": "/set_role — Выдать роль пользователю (user | admin)",