fix(traffic): correct misleading add-traffic note — 30-day validity

The buy-traffic warning said purchased traffic "does not carry over to the next
period", which contradicts how add-ons actually work: a package lives 30 days
and stays in the limit across the monthly reset within those 30 days. Reword to
"valid for 30 days from purchase" (ru/en/zh/fa) so users aren't misled.

src/locales/en.json

@@ -579,7 +579,7 @@
       "buyTraffic": "Buy more traffic",
       "currentTrafficLimit": "Current limit: {{limit}} GB (used {{used}} GB)",
       "buyTrafficTitle": "Buy more traffic",
-      "trafficWarning": "Purchased traffic is added to your current limit and does not carry over to the next period",
+      "trafficWarning": "Purchased traffic is added to your current limit and is valid for 30 days from purchase",
       "trafficUnavailable": "Traffic purchase is not available for your tariff",
       "unlimited": "Unlimited",
       "buyTrafficGb": "Buy {{gb}} GB",

src/locales/fa.json

@@ -429,7 +429,7 @@
       "buyTraffic": "خرید ترافیک بیشتر",
       "currentTrafficLimit": "محدودیت فعلی: {{limit}} GB (مصرف شده {{used}} GB)",
       "buyTrafficTitle": "خرید ترافیک بیشتر",
-      "trafficWarning": "ترافیک خریداری شده به محدودیت فعلی اضافه می‌شود و به دوره بعدی منتقل نمی‌شود",
+      "trafficWarning": "ترافیک خریداری‌شده به محدودیت فعلی اضافه می‌شود و تا ۳۰ روز از زمان خرید معتبر است",
       "trafficUnavailable": "خرید ترافیک برای اشتراک شما در دسترس نیست",
       "unlimited": "نامحدود",
       "buyTrafficGb": "خرید {{gb}} GB",

src/locales/ru.json

@@ -608,7 +608,7 @@
       "buyTraffic": "Докупить трафик",
       "currentTrafficLimit": "Текущий лимит: {{limit}} ГБ (использовано {{used}} ГБ)",
       "buyTrafficTitle": "Докупить трафик",
-      "trafficWarning": "Докупленный трафик добавляется к текущему лимиту и не переносится на следующий период",
+      "trafficWarning": "Докупленный трафик добавляется к текущему лимиту и действует 30 дней с момента покупки",
       "trafficUnavailable": "Докупка трафика недоступна для вашего тарифа",
       "unlimited": "Безлимит",
       "buyTrafficGb": "Купить {{gb}} ГБ",

src/locales/zh.json

@@ -429,7 +429,7 @@
       "buyTraffic": "购买更多流量",
       "currentTrafficLimit": "当前限制：{{limit}} GB（已使用 {{used}} GB）",
       "buyTrafficTitle": "购买更多流量",
-      "trafficWarning": "购买的流量将添加到当前限制，不会延续到下一个周期",
+      "trafficWarning": "购买的流量将添加到当前限制，自购买之日起30天内有效",
       "trafficUnavailable": "您的套餐不支持购买流量",
       "unlimited": "无限制",
       "buyTrafficGb": "购买 {{gb}} GB",