feat(i18n): add multi-language support (en/zh) across app and server

Implement useLocale composable and shared translation dictionaries
Translate public pages, booking flow, and receipt views
Store booking locale to send localized WhatsApp notifications

app/utils/formatters.ts

@@ -1,9 +1,11 @@
-export function formatDateTime(value: string | null, fallback = 'Not available') {
+import type { AppLocale } from '~~/shared/i18n'
+
+export function formatDateTime(value: string | null, fallback = 'Not available', locale: AppLocale = 'en') {
   if (!value) {
     return fallback
   }
 
-  return new Intl.DateTimeFormat('en-MY', {
+  return new Intl.DateTimeFormat(locale === 'zh' ? 'zh-MY' : 'en-MY', {
     dateStyle: 'medium',
     timeStyle: 'short'
   }).format(new Date(value))