fix: 恢复表格分页大小 localStorage 持久化

- usePersistedPageSize: 恢复 localStorage 读写，以系统配置为 fallback
- useTableLoader: handlePageSizeChange 时写入 localStorage
- Pagination.vue: handlePageSizeChange 时写入 localStorage

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

frontend/src/components/common/Pagination.vue

@@ -123,6 +123,7 @@ import { useI18n } from 'vue-i18n'
 import Icon from '@/components/icons/Icon.vue'
 import Select from './Select.vue'
 import { getConfiguredTablePageSizeOptions, normalizeTablePageSize } from '@/utils/tablePreferences'
+import { setPersistedPageSize } from '@/composables/usePersistedPageSize'
 
 const { t } = useI18n()
 
@@ -224,6 +225,7 @@ const goToPage = (newPage: number) => {
 const handlePageSizeChange = (value: string | number | boolean | null) => {
   if (value === null || typeof value === 'boolean') return
   const newPageSize = normalizeTablePageSize(typeof value === 'string' ? parseInt(value, 10) : value)
+  setPersistedPageSize(newPageSize)
   emit('update:pageSize', newPageSize)
 }