task-9(壳层/路由): 实现路由 meta 菜单 key 约定与 RouteMeta 类型增强

新增 src/types/vue-router.d.ts 模块增强(RouteMeta.title/menuKey)，meta.ts 提供
metaMenuKey/命名校验，router 守卫改类型化访问去掉 as cast，AdminLayout 标题同步
去 cast；校验首批注册表 menuKey 合规。

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

@@ -15,7 +15,7 @@ const collapsed = ref(false)
 const activePath = computed(() => route.path)
 const menuEntries = computed(() => toSidebarEntries(session.menuTree))
 const openedKeys = computed(() => groupKeysForActive(menuEntries.value, route.path))
-const pageTitle = computed(() => pageTitleOf(route.meta.title as string | undefined))
+const pageTitle = computed(() => pageTitleOf(route.meta.title))
 const userVm = computed(() => topbarUserOf(session.user))
 const logoUrl = joinAdminPath('assets', 'logo.jpg')