feat: Vike +data 服务端取数 / SEO Head 移植 / 404 错误页 / 服务端 DOM 模拟

- feedData.ts 聚合首页/板块/帖子详情数据，缺失内容 throw render(404)
- Go 侧 spa_meta/seo 的 head 生成逻辑移植到 src/ssr/head.ts
- _error 页复用站点壳渲染 404，+data 从 abortReason 恢复壳层数据
- linkedom 模拟服务端 DOM，DOMPurify 封装为 SSR 透传的 sanitizeHtml
- 新增 /api/home-boot 聚合端点（handler/home_boot.go）供 SSR 冷启动灌缓存

frontend/renderer/+onRenderHtml.tsx

@@ -2,10 +2,15 @@ import type { ComponentType, ReactElement } from 'react';
 import { renderToReadableStream } from 'react-dom/server';
 import { escapeInject, dangerouslySkipEscape } from 'vike/server';
 import type { PageContextServer } from 'vike/types';
-import App from '../src/App';
 import { createHomeStore } from '../src/store/homeStore';
 import { createRequestScope } from '../src/ssr/scopeTypes';
 import { runWithScope } from '../src/ssr/scope';
+import { seedFeedData, type FeedData } from '../src/ssr/feedData';
+import { renderHeadTags } from '../src/ssr/head';
+import { installServerDom } from '../src/ssr/serverDom';
+
+// 服务端 DOM polyfill：内容处理依赖 DOMParser/document，须在渲染前安装
+installServerDom();
 
 export { onRenderHtml };
 
@@ -32,6 +37,7 @@ async function renderPageToString(element: ReactElement): Promise<string> {
 
 async function onRenderHtml(pageContext: PageContextServer) {
   const Page = pageContext.Page as PageComponent | undefined;
+  const data = (pageContext as { data?: FeedData }).data;
 
   let pageHtml = '';
   if (Page) {
@@ -41,20 +47,26 @@ async function onRenderHtml(pageContext: PageContextServer) {
     const { pathname, searchOriginal } = pageContext.urlParsed;
     const url = pathname + (searchOriginal ?? '');
     try {
-      pageHtml = await runWithScope(scope, () => renderPageToString(<Page url={url} />));
+      pageHtml = await runWithScope(scope, () => {
+        // 渲染前把 +data 取回的数据 seed 进请求作用域（缓存层按 scope 隔离）
+        seedFeedData(data);
+        return renderPageToString(<Page url={url} />);
+      });
     } catch (err) {
       console.error('[j13] SSR 渲染失败，降级 SPA 壳:', err);
       pageHtml = '';
     }
   }
 
+  const headTags = renderHeadTags(data?.head);
+
+  // 404/301 等状态码由 Vike abort 机制（throw render/redirect）原生处理
   return escapeInject`<!DOCTYPE html>
 <html lang="zh-CN">
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
-    <meta name="description" content="拾三一隅，自在交流" />
-    <title>姜十三论坛 - 拾三一隅，自在交流</title>
+    ${dangerouslySkipEscape(headTags)}
     <script>${dangerouslySkipEscape(THEME_INIT_SCRIPT)}</script>
     <script>${dangerouslySkipEscape(ZOOM_BLOCK_SCRIPT)}</script>
   </head>