fix: 修复首页空白、小红书/游记封面图、定制页二维码

1. 首页大面积空白：useScrollReveal 添加 MutationObserver，
   确保异步子组件的 .reveal 元素也能触发入场动画

2. 小红书/游记封面图不显示：
   - 小红书 CDN 签名链接过期+防盗链，全部下载到本地
   - 新增 download-covers.mjs 脚本批量下载封面
   - 新增 useImageProxy composable 转换外部 URL
   - 页面 img 标签添加 referrerpolicy="no-referrer"
   - 管理端保存时自动下载外部封面图到本地
   - 种子数据更新为本地路径

3. 定制页微信号文字替换为二维码图片

4. prerender 路由添加 /xiaohongshu 和 /youji

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/api/admin/download-image.post.js

@@ -0,0 +1,91 @@
+import { writeFileSync, existsSync, mkdirSync } from 'fs'
+import { join } from 'path'
+import { requireAdmin } from '../../utils/auth.js'
+
+/**
+ * 下载外部图片到本地
+ * POST /api/admin/download-image
+ * Body: { url: "https://..." }
+ * Returns: { localUrl: "/uploads/covers/xxx.webp" }
+ */
+
+const ALLOWED_HOSTS = [
+  'sns-webpic-qc.xhscdn.com',
+  'ci.xiaohongshu.com',
+  'sns-img-bd.xhscdn.com',
+]
+
+/**
+ * 将签名 CDN URL 转为永久可下载的 URL
+ */
+function toPermanentUrl(url) {
+  try {
+    const parsed = new URL(url)
+    if (parsed.hostname === 'sns-webpic-qc.xhscdn.com') {
+      const parts = parsed.pathname.split('/')
+      if (parts.length >= 4) {
+        const imagePath = parts.slice(3).join('/')
+        return `https://ci.xiaohongshu.com/${imagePath}`
+      }
+    }
+  } catch {}
+  return url
+}
+
+export default defineEventHandler(async (event) => {
+  requireAdmin(event)
+
+  const { url } = await readBody(event)
+  if (!url || !url.startsWith('http')) {
+    throw createError({ statusCode: 400, message: '请提供有效的图片 URL' })
+  }
+
+  // 验证域名白名单
+  let parsedUrl
+  try {
+    parsedUrl = new URL(url)
+  } catch {
+    throw createError({ statusCode: 400, message: '无效的 URL' })
+  }
+
+  if (!ALLOWED_HOSTS.includes(parsedUrl.hostname)) {
+    throw createError({ statusCode: 403, message: '该域名不支持自动下载，请手动上传图片' })
+  }
+
+  // 生成本地文件名
+  const pathParts = parsedUrl.pathname.split('/')
+  const imageId = pathParts[pathParts.length - 1].split('!')[0] || `img-${Date.now()}`
+  const filename = `${imageId}.webp`
+  const coversDir = join(process.cwd(), 'public', 'uploads', 'covers')
+
+  if (!existsSync(coversDir)) {
+    mkdirSync(coversDir, { recursive: true })
+  }
+
+  const localPath = join(coversDir, filename)
+  const localUrl = `/uploads/covers/${filename}`
+
+  // 如果已下载过，直接返回
+  if (existsSync(localPath)) {
+    return { localUrl }
+  }
+
+  // 下载图片
+  const downloadUrl = toPermanentUrl(url)
+  try {
+    const res = await fetch(downloadUrl, {
+      headers: {
+        'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36',
+      },
+    })
+    if (!res.ok) {
+      throw createError({ statusCode: 502, message: `图片下载失败 (${res.status})` })
+    }
+    const buffer = Buffer.from(await res.arrayBuffer())
+    writeFileSync(localPath, buffer)
+    return { localUrl }
+  } catch (err) {
+    if (err.statusCode) throw err
+    throw createError({ statusCode: 502, message: `图片下载出错: ${err.message}` })
+  }
+})