Add hand-rolled English support (/en/*) alongside the Italian site

PocketBase gains optional, manually-authored English fields on articles
and categories (same record, same slug), and the frontend serves an /en
counterpart of every dynamic route via thin page wrappers around shared
view components — no i18n library, consistent with the project's existing
minimalism stance for a two-locale site with ~20 UI strings.

An article/category with no translation 404s cleanly on its own /en
detail page and is filtered out of /en listings, and the header's
language-switch link falls back to the English blog index rather than a
dead link; resolving that requires a global route middleware, since the
layout's header renders before the page content in document order and so
can't react to state a page component sets during its own async setup.

frontend/server/routes/content/articles/[slug].get.ts

@@ -1,15 +1,22 @@
 import type { Article, Category } from '#shared/types/blog'
 
+interface RawCategory extends Category {
+  nameEn?: string | null
+}
+
 interface RawArticle {
   id: string
   title: string
+  titleEn: string | null
   slug: string
   publishedAt: string
   content: string | null
+  contentEn: string | null
   cover: string
   coverAlt: string | null
+  coverAltEn: string | null
   authorName: string | null
-  expand?: { category?: Category }
+  expand?: { category?: RawCategory }
 }
 
 export default defineEventHandler(async (event): Promise<Article> => {
@@ -19,6 +26,8 @@ export default defineEventHandler(async (event): Promise<Article> => {
     throw createError({ statusCode: 400, statusMessage: 'Missing article slug' })
   }
 
+  const lang = langParam(getQuery(event).lang)
+
   const response = await pbFetch<PbList<RawArticle>>(
     `/api/collections/articles/records?fields=${ARTICLE_DETAIL_FIELDS}&expand=category&filter=${encodeURIComponent(`slug = ${quote(slug)}`)}&${pagination(1, 1)}`
   )
@@ -29,14 +38,37 @@ export default defineEventHandler(async (event): Promise<Article> => {
     throw createError({ statusCode: 404, statusMessage: 'Article not found' })
   }
 
+  const hasTranslation = Boolean(article.titleEn && article.contentEn)
+
+  // An /en/ request for an article with no translation yet 404s cleanly,
+  // rather than silently falling back to Italian text on an English URL —
+  // see docs/content-model.md.
+  if (lang === 'en' && !hasTranslation) {
+    throw createError({ statusCode: 404, statusMessage: 'Article not found' })
+  }
+
+  const title = lang === 'en' ? article.titleEn! : article.title
+  const content = lang === 'en' ? article.contentEn : article.content
+  const coverAlt = lang === 'en' ? article.coverAltEn || article.coverAlt : article.coverAlt
+  const category = article.expand?.category
+    ? {
+        name:
+          lang === 'en'
+            ? article.expand.category.nameEn || article.expand.category.name
+            : article.expand.category.name,
+        slug: article.expand.category.slug,
+      }
+    : null
+
   return {
-    title: article.title,
+    title,
     slug: article.slug,
     publishedAt: article.publishedAt,
-    cover: toMediaImage('articles', article.id, article.cover, article.coverAlt),
-    category: article.expand?.category ?? null,
-    html: renderMarkdown(article.content),
-    summary: summarise(article.content),
+    cover: toMediaImage('articles', article.id, article.cover, coverAlt),
+    category,
+    html: renderMarkdown(content),
+    summary: summarise(content),
     author: article.authorName || null,
+    hasTranslation,
   }
 })