Add i18n foundation (fa-IR/en-US) and localize landing + auth.

Introduce path-prefixed locale routing under app/[lang] with a middleware
that detects locale from cookie/Accept-Language (default fa-IR) and
redirects. Add fa-IR (source of truth) and en-US dictionaries, a server
getDictionary, a client I18nProvider/useT, locale-aware Link + router
helpers, and a language switcher. The root [lang] layout sets html
lang/dir and the per-locale font (Peyda for fa, Inter for en).

Landing sections and the login/register/auth shell now read all copy from
the dictionaries; dashboard localization follows in a later commit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/landing/sections/Footer.tsx

@@ -1,23 +1,27 @@
-import Link from 'next/link';
+'use client';
+
+import { Link } from '@/i18n/Link';
 import { Logo } from '../Logo';
+import { useT } from '@/i18n/I18nProvider';
 
 export function Footer() {
+  const t = useT();
   return (
     <footer className="relative border-t border-white/15 bg-slate-950/35 px-6 py-12 backdrop-blur-md">
       <div className="mx-auto flex max-w-6xl flex-col items-center justify-between gap-6 sm:flex-row">
         <Logo className="abrban-ink" />
         <nav className="abrban-ink flex items-center gap-6 text-sm text-white/80">
           <Link href="/login" className="transition hover:text-white">
-            ورود
+            {t.common.login}
           </Link>
           <Link href="/register" className="transition hover:text-white">
-            ثبت‌نام
+            {t.common.register}
           </Link>
           <Link href="/dashboard" className="transition hover:text-white">
-            داشبورد
+            {t.common.dashboard}
           </Link>
         </nav>
-        <p className="abrban-ink text-sm text-white/70">© ابربان — همهٔ حقوق محفوظ است</p>
+        <p className="abrban-ink text-sm text-white/70">{t.landing.footer.copyright}</p>
       </div>
     </footer>
   );