fix: 管理员重置配额补全 monthly 字段并修复 ristretto 缓存异步问题

- 后端 handler：ResetSubscriptionQuotaRequest 新增 Monthly 字段，
  验证逻辑扩展为 daily/weekly/monthly 至少一项为 true
- 后端 service：AdminResetQuota 新增 resetMonthly 参数，
  调用 ResetMonthlyUsage；重置后追加 subCacheL1.Wait()，
  保证 ristretto Del() 的异步删除立即生效，消除重置后
  /v1/usage 返回旧用量数据的竞态窗口
- 后端测试：更新存量测试用例匹配新签名，补充
  TestAdminResetQuota_ResetMonthlyOnly /
  TestAdminResetQuota_ResetMonthlyUsageError 两个新用例
- 前端 API：resetQuota options 类型新增 monthly: boolean
- 前端视图：confirmResetQuota 改为同时重置 daily/weekly/monthly
- i18n：中英文确认提示文案更新，提及每月配额

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/i18n/locales/en.ts

@@ -1574,7 +1574,7 @@ export default {
       revoke: 'Revoke',
       resetQuota: 'Reset Quota',
       resetQuotaTitle: 'Reset Usage Quota',
-      resetQuotaConfirm: "Reset the daily and weekly usage quota for '{user}'? Usage will be zeroed and windows restarted from today.",
+      resetQuotaConfirm: "Reset the daily, weekly, and monthly usage quota for '{user}'? Usage will be zeroed and windows restarted from today.",
       quotaResetSuccess: 'Quota reset successfully',
       failedToResetQuota: 'Failed to reset quota',
       noSubscriptionsYet: 'No subscriptions yet',