refactor(styles): 建立统一的生产级样式体系 (#4)

## 变更内容

- 将全局样式拆分为设计令牌、基础规则和语义组件层
- 集中管理 Naive UI 主题配置
- 迁移页面容器、表单、信息面板和按钮等重复样式
- 增加样式体系文档与自动契约检查

## 验证

- `npm run check:styles`
- `npm run build`Reviewed-on: #4

src/views/system/AuthRequiredView.vue

@@ -28,12 +28,12 @@ const description = computed(() => {
 </script>
 
 <template>
-  <div class="flex min-h-[calc(100vh-4rem)] items-center justify-center px-4 py-10">
-    <div class="w-full max-w-2xl border border-slate-200 bg-white px-8 py-14 text-center shadow-sm">
+  <div class="oc-system-page">
+    <div class="oc-system-card">
       <div class="text-7xl leading-none">🔐</div>
       <p class="mt-6 text-sm font-medium uppercase tracking-[0.24em] text-sky-600">401 Login Required</p>
-      <h1 class="mt-3 text-4xl font-bold text-slate-900">{{ title }}</h1>
-      <p class="mx-auto mt-4 max-w-xl text-sm leading-7 text-slate-600">
+      <h1 class="oc-page-title">{{ title }}</h1>
+      <p class="oc-page-description mx-auto max-w-xl">
         {{ description }}
       </p>