feat(admin): add initial admin dashboard structure

This commit introduces the foundational structure for the new admin dashboard.

- Utilizes @nuxt/ui to build the dashboard layout, including a collapsible sidebar and navigation.
- Adds initial pages for the dashboard, news, events, and hall of fame management.
- Implements a composable `useDashboardSidebarLinks` for managing sidebar navigation.
- Refactors the default layout by integrating the header and footer directly.
- Swaps the primary and secondary theme colors across the application.

app/layouts/admin-dashboard.vue

@@ -0,0 +1,44 @@
+<template>
+  <UDashboardGroup>
+    <UDashboardSidebar id="default" :open="sidebarOpen" collapsible resizable>
+      <template #header="{ collapsed }">
+        <div class="font-bold flex items-center">
+          <img src="/Logo.svg" alt="YPHS Alumni" class="h-8">
+          <span class="ml-2" v-if="!collapsed">永平中学校友会官网</span>
+        </div>
+      </template>
+
+      <template #default="{ collapsed }">
+        <UDashboardSearchButton :collapsed="collapsed" icon="mdi:magnify" class="bg-transparent ring-default" />
+
+        <UNavigationMenu :collapsed="collapsed" :items="sidebarLinks" orientation="vertical" tooltip popover />
+      </template>
+
+      <template #footer="{ collapsed }">
+      </template>
+    </UDashboardSidebar>
+
+    <UDashboardSearch :groups="groups" />
+
+    <slot />
+
+  </UDashboardGroup>
+</template>
+
+<script lang="ts" setup>
+const sidebarOpen = ref(false);
+
+const groups = ref([]);
+
+const { sidebarLinks } = useDashboardSidebarLinks();
+
+const route = useRoute();
+
+// 🪄 自动根据路由 name 或 meta 显示标题
+const pageTitle = computed(() => {
+  // 如果路由定义了 meta.title 优先用它，否则用 name
+  return route.meta.title || route.name || '首页'
+})
+</script>
+
+<style></style>