feat(i18n): /en/ 双语骨架——路由/切换/hreflang/回退/AI 标注

- astro i18n（zh 默认无前缀，en /en/）+ locale.ts 路径工具
- Header 语言切换（同路径跨前缀跳转，预构建毫秒级）
- /en/index + /en/archives/{slug}（postsEn 优先，缺译回退 zh 正文
  + AiTranslatedBadge 虚线标注 TMT）；en RSS（标题回退同策略）
- BaseLayout hreflang 双向 + x-default 指向 zh 源
- posts-en 集合（postsSchema.extend locked 润色锁）
- 坑：ts 端点文件误带 --- 开头会以 undefined:2:7 报 Unexpected token

验证: astro build 18 页 exit 0；/en/ 六文章路由+首页+rss 产物断言过；
      zh 侧零回归（11 页不变）；hreflang 抽查 dist/index.html

Spec: 2026-10-25_add-blog-i18n
Co-authored-by: GLM-5.3

src/pages/en/archives/[...slug].astro

@@ -0,0 +1,71 @@
+---
+// /en/archives/{slug}：英文版文章页——postsEn 优先；缺译回退 zh 正文 + 醒目标注
+import type { CollectionEntry } from 'astro:content';
+import { getCollection, render } from 'astro:content';
+import BaseLayout from '../../../layouts/BaseLayout.astro';
+import ArtalkComments from '../../../components/ArtalkComments.astro';
+import AiTranslatedBadge from '../../../components/AiTranslatedBadge.astro';
+import { t } from '../../../i18n/ui';
+
+export async function getStaticPaths() {
+  const zh = (await getCollection('posts', ({ data }) => !data.draft)).sort(
+    (a, b) => b.data.pubDate.getTime() - a.data.pubDate.getTime(),
+  );
+  const en = new Map((await getCollection('postsEn')).map((e) => [e.id, e]));
+  return zh.map((entry, i) => ({
+    params: { slug: entry.id },
+    props: { entry, enEntry: en.get(entry.id) ?? null, prev: zh[i + 1] ?? null, next: zh[i - 1] ?? null },
+  }));
+}
+
+interface Props {
+  entry: CollectionEntry<'posts'>;
+  enEntry: CollectionEntry<'postsEn'> | null;
+  prev: CollectionEntry<'posts'> | null;
+  next: CollectionEntry<'posts'> | null;
+}
+const { entry, enEntry, prev, next } = Astro.props;
+// 译文存在则渲染译文；否则回退 zh 正文（语言切换的降级承诺：单篇未译不破站）
+const { Content } = await render(enEntry ?? entry);
+const isReading = entry.data.category === 'reading';
+const date = entry.data.pubDate.toISOString().slice(0, 10);
+const words = (enEntry?.body ?? entry.body ?? '').split(/\s+/).length;
+const minutes = Math.max(1, Math.ceil(words / 220));
+---
+
+<BaseLayout title={`${enEntry?.data.title ?? entry.data.title} · wait4x`} track={isReading ? 'reading' : 'tech'}>
+  <article class={`post ${isReading ? 'post-reading' : 'post-tech'}`}>
+    <header class="post-head">
+      <p class="post-cat">
+        {isReading ? t('category_reading', 'en') : entry.data.category === 'tech' ? t('category_tech', 'en') : t('category_photo', 'en')}
+      </p>
+      <h1 class="post-title">{enEntry?.data.title ?? entry.data.title}</h1>
+      <p class="post-meta">
+        <i class="emo" style={`background:${entry.data.mood ?? 'var(--mood)'}`} aria-hidden="true" />
+        <time datetime={entry.data.pubDate.toISOString()}>{date}</time>
+        <span aria-hidden="true">·</span>
+        <span>{minutes} {t('reading_time_min', 'en')}</span>
+      </p>
+    </header>
+    <AiTranslatedBadge />
+    <div class={isReading ? 'prose-reading' : 'prose-tech'}>
+      <Content />
+    </div>
+    <nav class="pn">
+      {prev && <a class="pn-item" href={`/en/archives/${prev.id}/`}>← {t('prev_post', 'en')} · {prev.data.title}</a>}
+      {next && <a class="pn-item" href={`/en/archives/${next.id}/`}>{t('next_post', 'en')} · {next.data.title} →</a>}
+    </nav>
+    <ArtalkComments pageKey={`/archives/${entry.id}/`} pageTitle={entry.data.title} />
+  </article>
+</BaseLayout>
+
+<style>
+  .post-head { margin-bottom: var(--space-4); }
+  .post-cat { font-family: var(--font-mono); font-size: 12px; color: var(--ink-3); letter-spacing: 0.08em; }
+  .post-title { font-size: var(--text-h1); line-height: var(--leading-heading); color: var(--ink-1); text-wrap: balance; }
+  .post-meta { display: flex; align-items: center; gap: var(--space-2); margin-top: var(--space-2); font-size: 13px; color: var(--ink-3); }
+  .emo { display: inline-block; width: 10px; height: 10px; border-radius: 50%; }
+  .pn { display: flex; flex-direction: column; gap: var(--space-2); margin-top: var(--space-5); }
+  .pn-item { font-size: 14px; color: var(--ink-2); transition: color var(--dur) var(--ease); }
+  .pn-item:hover { color: var(--accent); }
+</style>