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.

docs/architecture.md

@@ -32,6 +32,10 @@ See [caddy/Caddyfile](../caddy/Caddyfile). One site block on `{$PUBLIC_DOMAIN}`:
   uploads).
 - everything else → `frontend:3000`.
 
+This means the English routes under `/en/*` ([frontend.md](./frontend.md#english-content))
+need **no Caddy changes** at all: they're plain Nuxt pages like any other, so they already fall
+under "everything else."
+
 `/admin` is **not** a Caddy rule: it's a Nitro route
 (`frontend/server/routes/admin.get.ts`) that redirects to `${pocketbaseUrl}/_/` (PocketBase's own
 fixed dashboard route, since it can't be told to serve elsewhere). Handling it in Nitro rather