fix: show fallback when tariff has no available periods for renewal

When all periods are removed from a tariff, users saw an empty
purchase form with no way to renew. Now shows a message explaining
the situation and a button to choose a different tariff.

src/locales/en.json

@@ -346,6 +346,9 @@
     "daysBeforeExpiry_one": "{{count}} day before expiry",
     "daysBeforeExpiry_other": "{{count}} days before expiry",
     "selectPeriod": "Select Period",
+    "noPeriodsAvailable": "No available periods for renewal",
+    "noPeriodsAvailableHint": "The administrator has changed this plan's settings. Please choose a different plan to renew your subscription.",
+    "chooseDifferentTariff": "Choose a different plan",
     "selectTraffic": "Select Traffic",
     "selectServers": "Select Servers",
     "selectDevices": "Devices",

src/locales/fa.json

@@ -297,6 +297,9 @@
     "daysBeforeExpiry": "روز قبل از انقضا",
     "daysBeforeExpiry_other": "{{count}} روز قبل از انقضا",
     "selectPeriod": "انتخاب دوره",
+    "noPeriodsAvailable": "دوره‌ای برای تمدید موجود نیست",
+    "noPeriodsAvailableHint": "مدیر تنظیمات این طرح را تغییر داده است. لطفاً طرح دیگری را برای تمدید اشتراک خود انتخاب کنید.",
+    "chooseDifferentTariff": "انتخاب طرح دیگر",
     "selectTraffic": "انتخاب ترافیک",
     "selectServers": "انتخاب سرورها",
     "selectDevices": "انتخاب دستگاه‌ها",

src/locales/ru.json

@@ -365,6 +365,9 @@
     "daysBeforeExpiry_few": "{{count}} дня до окончания",
     "daysBeforeExpiry_many": "{{count}} дней до окончания",
     "selectPeriod": "Выберите период",
+    "noPeriodsAvailable": "Нет доступных периодов для продления",
+    "noPeriodsAvailableHint": "Администратор изменил настройки этого тарифа. Выберите другой тариф для продления подписки.",
+    "chooseDifferentTariff": "Выбрать другой тариф",
     "selectTraffic": "Выберите трафик",
     "selectServers": "Выберите серверы",
     "selectDevices": "Устройства",

src/locales/zh.json

@@ -297,6 +297,9 @@
     "daysBeforeExpiry": "到期前天数",
     "daysBeforeExpiry_other": "到期前 {{count}} 天",
     "selectPeriod": "选择时长",
+    "noPeriodsAvailable": "没有可用的续订周期",
+    "noPeriodsAvailableHint": "管理员已更改此套餐的设置。请选择其他套餐续订您的订阅。",
+    "chooseDifferentTariff": "选择其他套餐",
     "selectTraffic": "选择流量",
     "selectServers": "选择服务器",
     "selectDevices": "选择设备",

src/pages/SubscriptionPurchase.tsx

@@ -1123,6 +1123,33 @@ export default function SubscriptionPurchase() {
                         </div>
                       )}
 
+                      {/* No periods available fallback */}
+                      {selectedTariff.periods.length === 0 &&
+                        !useCustomDays &&
+                        !(
+                          selectedTariff.custom_days_enabled &&
+                          (selectedTariff.price_per_day_kopeks ?? 0) > 0
+                        ) && (
+                          <div className="rounded-xl border border-amber-500/30 bg-amber-500/10 p-4 text-center">
+                            <div className="mb-2 text-sm font-medium text-amber-400">
+                              {t('subscription.noPeriodsAvailable')}
+                            </div>
+                            <div className="text-xs text-dark-400">
+                              {t('subscription.noPeriodsAvailableHint')}
+                            </div>
+                            <button
+                              onClick={() => {
+                                setShowTariffPurchase(false);
+                                setSelectedTariff(null);
+                                setSelectedTariffPeriod(null);
+                              }}
+                              className="btn-secondary mt-3 px-4 py-2 text-sm"
+                            >
+                              {t('subscription.chooseDifferentTariff')}
+                            </button>
+                          </div>
+                        )}
+
                       {/* Custom days option */}
                       {selectedTariff.custom_days_enabled &&
                         (selectedTariff.price_per_day_kopeks ?? 0) > 0 && (