feat: 用户管理页面添加充值功能

- 后端新增 POST /app-users/:id/recharge API
- 前端新增独立的用户充值页面 (/admin/users/:id/recharge)
- 充值页面风格与添加用户/编辑用户页面一致
- 支持选择卡密类型和数量进行充值
- 永久会员显示提示不允许充值

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/plugins/i18n/zh.json

@@ -438,7 +438,25 @@
         "expired": "已过期",
         "daysLeft": "天剩余"
       },
-      "devices": "设备管理"
+      "devices": "设备管理",
+      "recharge": {
+        "title": "用户充值",
+        "pageDesc": "为用户使用卡密充值",
+        "description": "为用户「{username}」使用卡密充值",
+        "userInfo": "用户信息",
+        "userInfoDesc": "当前用户的基本信息",
+        "selectCard": "选择卡密",
+        "selectCardDesc": "选择卡密类型和数量",
+        "cardType": "卡密类型",
+        "selectCardType": "选择卡密类型",
+        "noCardTypes": "该应用暂无卡密类型",
+        "cardTypeRequired": "请选择卡密类型",
+        "cardQuantity": "充值数量",
+        "cardValue": "充值内容",
+        "confirm": "确认充值",
+        "success": "充值成功",
+        "failed": "充值失败"
+      }
     },
     "orders": {
       "title": "订单管理",