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>
keyhan