feat(frontend): 分页 pageSize 持久化到 localStorage，刷新后自动恢复

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/admin/RedeemView.vue

@@ -395,6 +395,7 @@ import { ref, reactive, computed, onMounted, onUnmounted, watch } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { useClipboard } from '@/composables/useClipboard'
+import { getPersistedPageSize } from '@/composables/usePersistedPageSize'
 import { adminAPI } from '@/api/admin'
 import { formatDateTime } from '@/utils/format'
 import type { RedeemCode, RedeemCodeType, Group, GroupPlatform, SubscriptionType } from '@/types'
@@ -532,7 +533,7 @@ const filters = reactive({
 })
 const pagination = reactive({
   page: 1,
-  page_size: 20,
+  page_size: getPersistedPageSize(),
   total: 0,
   pages: 0
 })