feat(web): add i18n locale routes and language switcher component

Add locale-prefixed routes for admin, auth, dashboard, and public pages.
Add error, loading, and not-found pages for locale context. Add language
switcher UI component for Vietnamese/English toggle.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/[locale]/(public)/layout.tsx

@@ -0,0 +1,125 @@
+'use client';
+
+import { usePathname } from 'next/navigation';
+import { useTranslations } from 'next-intl';
+import { Button } from '@/components/ui/button';
+import { LanguageSwitcher } from '@/components/ui/language-switcher';
+import { Link } from '@/i18n/navigation';
+import { useAuthStore } from '@/lib/auth-store';
+import { cn } from '@/lib/utils';
+
+export default function PublicLayout({ children }: { children: React.ReactNode }) {
+  const pathname = usePathname();
+  const { user } = useAuthStore();
+  const t = useTranslations();
+
+  return (
+    <div className="min-h-screen bg-background">
+      <header
+        role="banner"
+        className="sticky top-0 z-50 border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60"
+      >
+        <div className="mx-auto flex h-14 max-w-7xl items-center px-4">
+          <Link href="/" className="mr-6 flex items-center space-x-2">
+            <span className="text-lg font-bold text-primary">{t('common.goodgo')}</span>
+          </Link>
+
+          <nav aria-label={t('nav.mainNav')} className="flex items-center space-x-1">
+            <Link
+              href="/"
+              className={cn(
+                'rounded-md px-3 py-2 text-sm font-medium transition-colors hover:bg-accent hover:text-accent-foreground',
+                pathname === '/' || pathname.match(/^\/(vi|en)\/?$/)
+                  ? 'bg-accent text-accent-foreground'
+                  : 'text-muted-foreground',
+              )}
+            >
+              {t('nav.home')}
+            </Link>
+            <Link
+              href="/search"
+              className={cn(
+                'rounded-md px-3 py-2 text-sm font-medium transition-colors hover:bg-accent hover:text-accent-foreground',
+                pathname.includes('/search')
+                  ? 'bg-accent text-accent-foreground'
+                  : 'text-muted-foreground',
+              )}
+            >
+              {t('nav.search')}
+            </Link>
+          </nav>
+
+          <div className="ml-auto flex items-center space-x-2">
+            <LanguageSwitcher />
+            {user ? (
+              <>
+                <span className="hidden text-sm text-muted-foreground sm:inline">
+                  {user.fullName}
+                </span>
+                <Link href="/dashboard">
+                  <Button size="sm">{t('common.dashboard')}</Button>
+                </Link>
+              </>
+            ) : (
+              <>
+                <Link href="/login">
+                  <Button variant="ghost" size="sm">
+                    {t('common.login')}
+                  </Button>
+                </Link>
+                <Link href="/register">
+                  <Button size="sm">{t('common.register')}</Button>
+                </Link>
+              </>
+            )}
+          </div>
+        </div>
+      </header>
+
+      <main id="main-content" role="main">
+        {children}
+      </main>
+
+      <footer role="contentinfo" className="border-t bg-muted/40">
+        <div className="mx-auto max-w-7xl px-4 py-8">
+          <div className="grid gap-8 sm:grid-cols-2 lg:grid-cols-4">
+            <div>
+              <h3 className="mb-3 text-sm font-semibold">{t('common.goodgo')}</h3>
+              <p className="text-sm text-muted-foreground">
+                {t('footer.description')}
+              </p>
+            </div>
+            <div>
+              <h3 className="mb-3 text-sm font-semibold">{t('footer.propertyTypes')}</h3>
+              <ul className="space-y-2 text-sm text-muted-foreground">
+                <li><Link href="/search?propertyType=APARTMENT" className="hover:text-foreground">{t('propertyTypes.APARTMENT')}</Link></li>
+                <li><Link href="/search?propertyType=HOUSE" className="hover:text-foreground">{t('propertyTypes.HOUSE')}</Link></li>
+                <li><Link href="/search?propertyType=VILLA" className="hover:text-foreground">{t('propertyTypes.VILLA')}</Link></li>
+                <li><Link href="/search?propertyType=LAND" className="hover:text-foreground">{t('propertyTypes.LAND')}</Link></li>
+              </ul>
+            </div>
+            <div>
+              <h3 className="mb-3 text-sm font-semibold">{t('footer.areas')}</h3>
+              <ul className="space-y-2 text-sm text-muted-foreground">
+                <li><Link href="/search?city=Hồ Chí Minh" className="hover:text-foreground">TP. Hồ Chí Minh</Link></li>
+                <li><Link href="/search?city=Hà Nội" className="hover:text-foreground">Hà Nội</Link></li>
+                <li><Link href="/search?city=Đà Nẵng" className="hover:text-foreground">Đà Nẵng</Link></li>
+                <li><Link href="/search?city=Nha Trang" className="hover:text-foreground">Nha Trang</Link></li>
+              </ul>
+            </div>
+            <div>
+              <h3 className="mb-3 text-sm font-semibold">{t('footer.support')}</h3>
+              <ul className="space-y-2 text-sm text-muted-foreground">
+                <li><Link href="/login" className="hover:text-foreground">{t('common.login')}</Link></li>
+                <li><Link href="/register" className="hover:text-foreground">{t('common.register')}</Link></li>
+              </ul>
+            </div>
+          </div>
+          <div className="mt-8 border-t pt-4 text-center text-sm text-muted-foreground">
+            {t('common.allRightsReserved')}
+          </div>
+        </div>
+      </footer>
+    </div>
+  );
+}