feat(frontend): 添加页面布局组件

布局组件：
- layouts/DefaultLayout.vue，默认布局组合

Layout 组件：
- components/Layout/AppHeader.vue，顶部导航栏（品牌、环境标签、搜索、用户信息）
- components/Layout/AppSidebar.vue，侧边菜单栏（导航菜单项）
- components/Layout/AppMain.vue，主内容区容器

布局结构：顶栏 + 侧边栏 + 内容区（CSS Grid）

frontend/src/components/Layout/AppSidebar.vue

@@ -0,0 +1,149 @@
+<template>
+  <aside class="sidebar">
+    <div class="nav-group">
+      <div class="nav-label">概览</div>
+      <router-link to="/dashboard" class="nav-item" active-class="active">
+        <span class="ic">▣</span>资源大盘
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">机房 &amp; 网络</div>
+      <router-link to="/resource/status" class="nav-item" active-class="active">
+        <span class="ic">⬡</span>资源状态看板
+      </router-link>
+      <router-link to="/cluster" class="nav-item" active-class="active">
+        <span class="ic">◆</span>集群 / 节点<span class="badge">7</span>
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">资源管理</div>
+      <router-link to="/resource/mgmt" class="nav-item" active-class="active">
+        <span class="ic">▥</span>资源管理<span class="badge">CMDB</span>
+      </router-link>
+      <router-link to="/service/mgmt" class="nav-item" active-class="active">
+        <span class="ic">◈</span>服务管理<span class="badge">Consul</span>
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">服务交付</div>
+      <router-link to="/service/catalog" class="nav-item" active-class="active">
+        <span class="ic">▤</span>基础服务目录
+      </router-link>
+      <router-link to="/tasks" class="nav-item" active-class="active">
+        <span class="ic">▧</span>任务中心<span class="badge">2</span>
+      </router-link>
+      <router-link to="/config" class="nav-item" active-class="active">
+        <span class="ic">⚙</span>配置中心管理<span class="badge">Apollo</span>
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">可观测性</div>
+      <router-link to="/monitor" class="nav-item" active-class="active">
+        <span class="ic">◎</span>监控 / 日志 / 告警
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">统一入口</div>
+      <router-link to="/subsystem" class="nav-item" active-class="active">
+        <span class="ic">↗</span>子系统导航
+      </router-link>
+    </div>
+    <div class="nav-group">
+      <div class="nav-label">审计</div>
+      <router-link to="/audit/login" class="nav-item" active-class="active">
+        <span class="ic">📋</span>登录审计
+      </router-link>
+      <router-link to="/audit/ops" class="nav-item" active-class="active">
+        <span class="ic">📝</span>运维操作审计
+      </router-link>
+    </div>
+    <div class="sidebar-foot">
+      xinfra v3 一期 · 七机房容器化<br>RKE2 · Calico BGP · Ceph · LAS<br>AWS TGW + WireGuard · LDAP 认证
+    </div>
+  </aside>
+</template>
+
+<script setup lang="ts">
+</script>
+
+<style scoped>
+.sidebar {
+  background: var(--bg-panel);
+  border-right: 1px solid var(--line);
+  padding: 14px 10px;
+  display: flex;
+  flex-direction: column;
+  overflow-y: auto;
+}
+
+.nav-group {
+  margin-bottom: 18px;
+}
+
+.nav-label {
+  font-size: 10.5px;
+  color: var(--text-dim);
+  text-transform: uppercase;
+  letter-spacing: 1px;
+  padding: 0 10px;
+  margin-bottom: 6px;
+  font-weight: 600;
+}
+
+.nav-item {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 8px 10px;
+  border-radius: 6px;
+  color: var(--text-mid);
+  font-size: 13px;
+  font-weight: 500;
+  cursor: pointer;
+  margin-bottom: 2px;
+  border: 1px solid transparent;
+  text-decoration: none;
+}
+
+.nav-item .ic {
+  width: 16px;
+  text-align: center;
+  font-size: 13px;
+  opacity: 0.85;
+}
+
+.nav-item:hover {
+  background: var(--bg-panel-2);
+  color: var(--text-hi);
+}
+
+.nav-item.active {
+  background: #13261F;
+  color: var(--accent);
+  border-color: var(--accent-dim);
+}
+
+.nav-item .badge {
+  margin-left: auto;
+  font-family: var(--mono);
+  font-size: 10px;
+  background: #262C38;
+  color: var(--text-dim);
+  padding: 1px 6px;
+  border-radius: 10px;
+}
+
+.nav-item.active .badge {
+  background: var(--accent-dim);
+  color: #CFFCE9;
+}
+
+.sidebar-foot {
+  margin-top: auto;
+  padding: 10px;
+  border-top: 1px solid var(--line-soft);
+  font-size: 11px;
+  color: var(--text-dim);
+  line-height: 1.6;
+}
+</style>