feat(i18n): 添加订阅管理教程指南英文翻译

在 en.ts 中为订阅管理页面新增 guide 相关翻译词条，
与中文翻译保持结构一致，支持中英文切换。
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/i18n/locales/en.ts

@@ -1759,7 +1759,37 @@ export default {
       pleaseSelectGroup: 'Please select a group',
       validityDaysRequired: 'Please enter a valid number of days (at least 1)',
       revokeConfirm:
-        "Are you sure you want to revoke the subscription for '{user}'? This action cannot be undone."
+        "Are you sure you want to revoke the subscription for '{user}'? This action cannot be undone.",
+      guide: {
+        title: 'Subscription Management Guide',
+        subtitle: 'Subscription mode lets you assign time-based usage quotas to users, with daily/weekly/monthly limits. Follow these steps to get started.',
+        showGuide: 'Usage Guide',
+        step1: {
+          title: 'Create a Subscription Group',
+          line1: 'Go to "Group Management" page, click "Create Group"',
+          line2: 'Set billing type to "Subscription", configure daily/weekly/monthly quota limits',
+          line3: 'Save the group and ensure its status is "Active"',
+          link: 'Go to Group Management'
+        },
+        step2: {
+          title: 'Assign Subscription to User',
+          line1: 'Click the "Assign Subscription" button in the top right',
+          line2: 'Search for a user by email and select them',
+          line3: 'Choose a subscription group, set validity days, then click "Assign"'
+        },
+        step3: {
+          title: 'Manage Existing Subscriptions'
+        },
+        actions: {
+          adjust: 'Adjust',
+          adjustDesc: 'Extend or shorten the subscription validity period',
+          resetQuota: 'Reset Quota',
+          resetQuotaDesc: 'Reset daily/weekly/monthly usage to zero',
+          revoke: 'Revoke',
+          revokeDesc: 'Immediately terminate the subscription (irreversible)'
+        },
+        tip: 'Tip: Only groups with billing type "Subscription" and status "Active" appear in the group dropdown. If no options are available, create one in Group Management first.'
+      }
     },
 
     // Accounts