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/zh.json

@@ -1584,6 +1584,22 @@
           "subscription": "• 禁止购买订阅",
           "reason": "原因"
         },
+        "promoGroup": "优惠组",
+        "noPromoGroup": "未设置",
+        "changePromoGroup": "更改",
+        "selectPromoGroup": "选择组",
+        "removePromoGroup": "移除",
+        "activePromoOffer": "活跃促销优惠",
+        "discount": "折扣",
+        "source": "来源",
+        "expiresAt": "到期时间",
+        "deactivateOffer": "停用",
+        "sendOffer": "发送优惠",
+        "discountPercent": "折扣 %",
+        "validHours": "有效期（小时）",
+        "offerSent": "优惠已发送",
+        "offerSendError": "发送优惠失败",
+        "offerDeactivated": "优惠已停用",
         "subscription": {
           "current": "当前订阅",
           "tariff": "套餐",