feat: show affected subscriptions count on tariff deletion

Update delete mutation to use affected_subscriptions from API response.
Show contextual success notification with subscription count.
Add deleteSuccessWithSubscriptions translation key in all 4 locales.

src/locales/zh.json

@@ -1114,6 +1114,7 @@
       "confirmDeleteText": "此操作不可撤销。套餐将被永久删除。",
       "confirmDeleteWithSubscriptions": "此套餐有 {{count}} 个活跃订阅。删除后，用户续订时需要选择新套餐。",
       "deleteSuccess": "套餐删除成功",
+      "deleteSuccessWithSubscriptions": "套餐已删除。{{count}} 个订阅已重置 — 用户续订时将选择新套餐。",
       "saveOrder": "保存排序",
       "orderSaved": "排序已保存",
       "dragToReorder": "拖动以重新排序",