Remove next-intl localization infrastructure

Strips out the i18n layer (next-intl, message files, language switcher,
provider) to reduce complexity. Nav components now use plain English strings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/layouts/observer-nav.tsx

@@ -2,22 +2,20 @@
 
 import { BarChart3, Home } from 'lucide-react'
 import { RoleNav, type NavItem, type RoleNavUser } from '@/components/layouts/role-nav'
-import { useTranslations } from 'next-intl'
 
 interface ObserverNavProps {
   user: RoleNavUser
 }
 
 export function ObserverNav({ user }: ObserverNavProps) {
-  const t = useTranslations('nav')
   const navigation: NavItem[] = [
     {
-      name: t('dashboard'),
+      name: 'Dashboard',
       href: '/observer',
       icon: Home,
     },
     {
-      name: t('reports'),
+      name: 'Reports',
       href: '/observer/reports',
       icon: BarChart3,
     },