task-11(壳层/路由): 实现无菜单权限空状态

empty-state 定义标题/引导文案与 shouldShowEmptyMenu 纯判定(Boolean 化防 undefined)；
AdminLayout 侧边栏与内容区(根路由)共用空态，加载中不闪现，未初始化不误报。

admin-frontend-vue/src/layout/AdminLayout.vue

@@ -6,6 +6,11 @@ import { useAdminSessionStore } from '@/stores/admin-session'
 import { joinAdminPath } from '@/config/app'
 import { pageTitleOf, topbarUserOf } from '@/layout/topbar-model'
 import { groupKeysForActive, toSidebarEntries } from '@/layout/menu-mapper'
+import {
+  EMPTY_MENU_DESCRIPTION,
+  EMPTY_MENU_TITLE,
+  shouldShowEmptyMenu,
+} from '@/layout/empty-state'
 
 const route = useRoute()
 const router = useRouter()
@@ -15,6 +20,7 @@ const collapsed = ref(false)
 const activePath = computed(() => route.path)
 const menuEntries = computed(() => toSidebarEntries(session.menuTree))
 const openedKeys = computed(() => groupKeysForActive(menuEntries.value, route.path))
+const emptyMenu = computed(() => shouldShowEmptyMenu(menuEntries.value.length > 0, session.loading, session.initialized))
 const pageTitle = computed(() => pageTitleOf(route.meta.title))
 const userVm = computed(() => topbarUserOf(session.user))
 const logoUrl = joinAdminPath('assets', 'logo.jpg')
@@ -55,7 +61,7 @@ async function signOut() {
             </el-menu-item>
           </template>
         </el-menu>
-        <el-empty v-if="!menuEntries.length && !session.loading" description="暂无可用菜单" :image-size="72" />
+        <el-empty v-if="emptyMenu" :description="EMPTY_MENU_TITLE" :image-size="72" />
       </el-scrollbar>
 
       <button class="sidebar-collapse" type="button" @click="collapsed = !collapsed">
@@ -79,7 +85,13 @@ async function signOut() {
       </header>
       <main class="admin-content">
         <el-alert v-if="session.error" :title="session.error" type="error" show-icon :closable="false" />
-        <RouterView />
+        <el-empty
+          v-if="emptyMenu && route.path === '/'"
+          :title="EMPTY_MENU_TITLE"
+          :description="EMPTY_MENU_DESCRIPTION"
+          :image-size="96"
+        />
+        <RouterView v-else />
       </main>
     </section>
   </div>