feat(client): 初始化前端壳与鉴权守卫（P1-5）

- 技术栈：React 18 + TypeScript + Vite + Tailwind

- API 层：ApiError + 401 自动刷新 + single-flight 重试

- 鉴权：内存 Access Token + Cookie Refresh + 启动 bootstrap

- RBAC：权限映射 + RequireAuth/RequirePermission 路由守卫

- 布局：OA 工作台壳层 + 侧边栏 + 5 个占位页面

- 样式：复用 hyb-web 视觉 token（单向同步）

- 文档：新增 client README，补充 server 联调说明

client/src/components/common/EmptyStateCard.tsx

@@ -0,0 +1,17 @@
+import type { ReactNode } from "react";
+
+type EmptyStateCardProps = {
+  title: string;
+  description: string;
+  footer?: ReactNode;
+};
+
+export function EmptyStateCard({ title, description, footer }: EmptyStateCardProps) {
+  return (
+    <section className="card-std">
+      <h3 className="card-title">{title}</h3>
+      <p className="card-desc">{description}</p>
+      {footer ? <div className="mt-4">{footer}</div> : null}
+    </section>
+  );
+}

client/src/components/common/PageHeader.tsx

@@ -0,0 +1,20 @@
+import type { ReactNode } from "react";
+
+type PageHeaderProps = {
+  title: string;
+  subtitle?: string;
+  actions?: ReactNode;
+};
+
+export function PageHeader({ title, subtitle, actions }: PageHeaderProps) {
+  return (
+    <div className="mb-6 flex flex-wrap items-start justify-between gap-4">
+      <div>
+        <h2 className="text-2xl font-bold text-slate-900">{title}</h2>
+        {subtitle ? <p className="mt-1 text-sm text-secondary">{subtitle}</p> : null}
+      </div>
+
+      {actions ? <div className="shrink-0">{actions}</div> : null}
+    </div>
+  );
+}