fix(后台订单): 会员变更摘要无账期时不再输出悬空分隔符

- AdminRechargeOrderPage 的会员变更摘要仅在存在账期时才追加 "/ 月付|年付"，避免输出 “新购 Pro / ”。

apps/admin-web/src/pages/AdminRechargeOrderPage.tsx

@@ -1308,10 +1308,9 @@ function formatMembershipChangeSummary(
     before && after && before !== after
       ? `${before}→${after}`
       : (after ?? before ?? '-');
-  const cycle = formatMembershipCycleKind(
-    change.cycleKindAfter ?? change.cycleKindBefore ?? '',
-  );
-  return `${action} ${planPath} / ${cycle}`;
+  const cycleKind = change.cycleKindAfter ?? change.cycleKindBefore;
+  const cycle = cycleKind ? ` / ${formatMembershipCycleKind(cycleKind)}` : '';
+  return `${action} ${planPath}${cycle}`;
 }
 
 function formatMoney(cents: number) {