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/index.css

@@ -0,0 +1,47 @@
+/*
+  Style tokens source (single-direction sync):
+  - /home/shunli/Projects/hyb-web
+  - commit: unavailable_local_reference
+*/
+
+@import url("https://fonts.googleapis.com/css2?family=Public+Sans:wght@400;500;700;900&display=swap");
+
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+@layer base {
+  body {
+    @apply bg-background-light text-slate-900 font-sans antialiased selection:bg-primary selection:text-white;
+  }
+
+  #root {
+    @apply min-h-screen;
+  }
+}
+
+@layer components {
+  .layout-container {
+    @apply mx-auto max-w-7xl px-4 sm:px-6 lg:px-8;
+  }
+
+  .btn-primary {
+    @apply rounded-lg bg-primary px-4 py-2 font-bold text-white transition-colors hover:bg-primary-600;
+  }
+
+  .btn-secondary {
+    @apply rounded-lg border border-slate-200 bg-white px-4 py-2 font-medium text-slate-700 transition-colors hover:bg-slate-50;
+  }
+
+  .card-std {
+    @apply rounded-xl border border-slate-200 bg-white p-6 text-left shadow-sm transition-all hover:shadow-md;
+  }
+
+  .card-title {
+    @apply mb-2 text-xl font-bold text-slate-900;
+  }
+
+  .card-desc {
+    @apply text-slate-600;
+  }
+}