fix(legal): show legal pages in site language with bidirectional toggle

Wire legal pages to LanguageContext, pass locale on footer/booking links,
translate layout chrome, and restore SSR content when switching back to English.

frontend/src/app/(public)/book/[eventId]/page.tsx

@@ -1370,7 +1370,7 @@ export default function BookingPage() {
                 >
                   {t('booking.form.termsAgreePart1')}
                   <Link
-                    href="/legal/terms-policy"
+                    href={`/legal/terms-policy${locale === 'es' ? '?locale=es' : ''}`}
                     target="_blank"
                     rel="noopener noreferrer"
                     className="text-secondary-blue hover:text-brand-navy underline"
@@ -1379,7 +1379,7 @@ export default function BookingPage() {
                   </Link>
                   {t('booking.form.termsAgreePart2')}
                   <Link
-                    href="/legal/privacy-policy"
+                    href={`/legal/privacy-policy${locale === 'es' ? '?locale=es' : ''}`}
                     target="_blank"
                     rel="noopener noreferrer"
                     className="text-secondary-blue hover:text-brand-navy underline"