fix: 修复授权页面卡类选项显示空括号问题

- 只有当 billing_type 有值时才显示括号内容
- 将"卡类权限"标签改为"选择卡类"，更清晰
- 添加 selectCardTypePlaceholder 翻译

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/plugins/i18n/en.json

@@ -1717,6 +1717,7 @@
         "selectAppPlaceholder": "Please select an application",
         "cardPermission": "Card Type Permissions",
         "selectCardType": "Select Card Type",
+        "selectCardTypePlaceholder": "Please select a card type",
         "addCardType": "Add",
         "cardTypeList": "Authorized Card Types",
         "cardTypeName": "Card Type Name",

frontend/src/plugins/i18n/zh.json

@@ -1706,6 +1706,7 @@
         "selectAppPlaceholder": "请选择应用",
         "cardPermission": "卡类权限",
         "selectCardType": "选择卡类",
+        "selectCardTypePlaceholder": "请选择卡类",
         "addCardType": "添加",
         "cardTypeList": "已授权卡类",
         "cardTypeName": "卡类名称",