feat: add promo group and promo offer management to AdminUserDetail

- Info tab: promo group card with inline dropdown to change/remove group
- Balance tab: active promo offer display with deactivate button
- Balance tab: send promo offer form (discount %, valid hours)
- Add deactivateDiscount API method to promocodesApi
- Add locale keys for ru/en/zh/fa
- Fix race condition in subscription create (stale state read)
- Fix unhandled promise in handleInlineConfirm
- Remove unused legacy adminUsers block from ru.json

src/locales/fa.json

@@ -1585,6 +1585,22 @@
           "subscription": "• خرید اشتراک ممنوع",
           "reason": "دلیل"
         },
+        "promoGroup": "گروه تبلیغاتی",
+        "noPromoGroup": "تنظیم نشده",
+        "changePromoGroup": "تغییر",
+        "selectPromoGroup": "انتخاب گروه",
+        "removePromoGroup": "حذف",
+        "activePromoOffer": "پیشنهاد فعال",
+        "discount": "تخفیف",
+        "source": "منبع",
+        "expiresAt": "انقضا",
+        "deactivateOffer": "غیرفعال کردن",
+        "sendOffer": "ارسال پیشنهاد",
+        "discountPercent": "تخفیف %",
+        "validHours": "مدت اعتبار (ساعت)",
+        "offerSent": "پیشنهاد ارسال شد",
+        "offerSendError": "خطا در ارسال پیشنهاد",
+        "offerDeactivated": "پیشنهاد غیرفعال شد",
         "subscription": {
           "current": "اشتراک فعلی",
           "tariff": "تعرفه",