feat: 更新网站页面和组件，新增多个页面（关于、专家、会员、政策等）

app/pages/downloads.vue

@@ -0,0 +1,22 @@
+<template>
+  <SectionStub
+    title="资料下载"
+    description="提供申报模板、政策文件、数据手册与成果简报等工具服务（可按权限分级开放）。"
+    :links="links"
+  />
+</template>
+
+<script setup lang="ts">
+import SectionStub from '@/components/SectionStub.vue'
+import { usePageSeo } from '@/composables/usePageSeo'
+
+usePageSeo({ title: '资料下载', description: '资料下载与模板入口。', path: '/downloads' })
+
+const links = [
+  { label: '申报模板', to: '/downloads?type=templates', desc: '会员/专家申请书等' },
+  { label: '政策文件', to: '/downloads?type=policies' },
+  { label: '数据手册', to: '/downloads?type=data' },
+  { label: '成果简报', to: '/downloads?type=briefs' }
+]
+</script>
+