feat: add external squad selection to tariff admin form

- Add ExternalSquadInfo type and getAvailableExternalSquads API method
- Add external_squad_uuid field to TariffDetail, TariffCreateRequest, TariffUpdateRequest
- Add radio-button external squad picker in Servers tab of tariff create/edit
- Add translations for external squad UI in all 4 locales (en, ru, zh, fa)

src/locales/en.json

@@ -1923,6 +1923,10 @@
       "noPeriodsHint": "No added periods. Add at least one period.",
       "daysShort": "d.",
       "serversTitle": "Servers",
+      "externalSquadTitle": "External Squad",
+      "externalSquadHint": "Assign a RemnaWave external squad for users on this tariff. When a subscription is created, the user will be automatically added to the selected squad.",
+      "noExternalSquad": "No external squad",
+      "externalSquadUsers": "users",
       "serversTabHint": "Select servers available on this tariff.",
       "noServersAvailable": "No servers available",
       "promoGroupsTitle": "Promo Groups",

src/locales/fa.json

@@ -1567,6 +1567,10 @@
       "noPeriodsHint": "هیچ دوره‌ای اضافه نشده. حداقل یک دوره اضافه کنید.",
       "daysShort": "روز",
       "serversTitle": "سرورها",
+      "externalSquadTitle": "گروه خارجی",
+      "externalSquadHint": "یک گروه خارجی RemnaWave برای کاربران این تعرفه تعیین کنید. هنگام ایجاد اشتراک، کاربر به طور خودکار به گروه انتخاب شده اضافه می‌شود.",
+      "noExternalSquad": "بدون گروه خارجی",
+      "externalSquadUsers": "کاربران",
       "serversTabHint": "سرورهای موجود در این تعرفه را انتخاب کنید.",
       "noServersAvailable": "هیچ سروری در دسترس نیست",
       "promoGroupsTitle": "گروه‌های تبلیغاتی",

src/locales/ru.json

@@ -2437,6 +2437,10 @@
       "noPeriodsHint": "Нет добавленных периодов. Добавьте хотя бы один период.",
       "daysShort": "дн.",
       "serversTitle": "Серверы",
+      "externalSquadTitle": "Внешний сквад",
+      "externalSquadHint": "Назначьте внешний сквад RemnaWave для пользователей этого тарифа. При создании подписки пользователь будет автоматически добавлен в выбранный сквад.",
+      "noExternalSquad": "Без внешнего сквада",
+      "externalSquadUsers": "пользователей",
       "serversTabHint": "Выберите серверы, доступные на этом тарифе.",
       "noServersAvailable": "Нет доступных серверов",
       "promoGroupsTitle": "Промо-группы",

src/locales/zh.json

@@ -1604,6 +1604,10 @@
       "noPeriodsHint": "没有添加的周期。请至少添加一个周期。",
       "daysShort": "天",
       "serversTitle": "服务器",
+      "externalSquadTitle": "外部小组",
+      "externalSquadHint": "为此套餐的用户分配RemnaWave外部小组。创建订阅时，用户将自动添加到所选小组。",
+      "noExternalSquad": "无外部小组",
+      "externalSquadUsers": "用户",
       "serversTabHint": "选择此套餐上可用的服务器。",
       "noServersAvailable": "没有可用的服务器",
       "promoGroupsTitle": "促销组",