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/utils/queries.ts

@@ -1,10 +1,13 @@
 /** PocketBase query fragments. Only the fields the pages actually render are requested. */
+import type { Locale } from '#shared/utils/locale'
 
 export const ARTICLE_SUMMARY_FIELDS =
-  'id,title,slug,publishedAt,cover,coverAlt,expand.category.name,expand.category.slug'
+  'id,title,titleEn,slug,publishedAt,cover,coverAlt,coverAltEn,expand.category.name,expand.category.nameEn,expand.category.slug'
 
 export const ARTICLE_DETAIL_FIELDS =
-  'id,title,slug,content,publishedAt,cover,coverAlt,authorName,expand.category.name,expand.category.slug'
+  'id,title,titleEn,slug,content,contentEn,publishedAt,cover,coverAlt,coverAltEn,authorName,expand.category.name,expand.category.nameEn,expand.category.slug'
+
+export const CATEGORY_FIELDS = 'name,nameEn,slug'
 
 export const PAGE_SIZE = 12
 
@@ -16,5 +19,8 @@ export const pageParam = (value: unknown): number => {
   return Number.isInteger(page) && page > 0 ? page : 1
 }
 
+/** Reads a `lang` query param, falling back to Italian for anything but `en`. */
+export const langParam = (value: unknown): Locale => (value === 'en' ? 'en' : 'it')
+
 /** Quotes a value for PocketBase's `filter` DSL, escaping embedded quotes. */
 export const quote = (value: string) => `"${value.replace(/"/g, '\\"')}"`