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/shared/utils/locale.ts

@@ -0,0 +1,16 @@
+export type Locale = 'it' | 'en'
+
+export const LOCALES: Locale[] = ['it', 'en']
+
+/** Prefixes a bare, unprefixed path (e.g. `/blog/mio-slug`) for the given locale. */
+export function localePath(locale: Locale, path: string): string {
+  if (locale !== 'en') return path
+  return path === '/' ? '/en' : `/en${path}`
+}
+
+/** Strips the `/en` prefix, if any, returning the bare Italian-equivalent path. */
+export function bareLocalePath(path: string): string {
+  if (path === '/en') return '/'
+  if (path.startsWith('/en/')) return path.slice(3)
+  return path
+}