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.

tests/support/pocketbase.ts

@@ -150,6 +150,8 @@ export async function startTestPocketbase(options: StartOptions = {}): Promise<T
         category: category?.id,
         publishedAt: article.publishedAt ?? '',
         authorName: article.authorName ?? '',
+        titleEn: article.titleEn ?? '',
+        contentEn: article.contentEn ?? '',
       }),
     })
     articles.push((await response.json()) as TestArticle)