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/composables/usePersistedPageSize.ts

@@ -0,0 +1,27 @@
+const STORAGE_KEY = 'table-page-size'
+const DEFAULT_PAGE_SIZE = 20
+
+/**
+ * 从 localStorage 读取/写入 pageSize
+ * 全局共享一个 key，所有表格统一偏好
+ */
+export function getPersistedPageSize(fallback = DEFAULT_PAGE_SIZE): number {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY)
+    if (stored) {
+      const parsed = Number(stored)
+      if (Number.isFinite(parsed) && parsed > 0) return parsed
+    }
+  } catch {
+    // localStorage 不可用（隐私模式等）
+  }
+  return fallback
+}
+
+export function setPersistedPageSize(size: number): void {
+  try {
+    localStorage.setItem(STORAGE_KEY, String(size))
+  } catch {
+    // 静默失败
+  }
+}