feat: send ticket receipts via WhatsApp and normalize phone numbers

Add WhatsApp API integration for automated receipt delivery
Enforce country codes for all phone number inputs (defaults to +60)

app/pages/management/users/index.vue

@@ -166,7 +166,7 @@
                 size="lg"
                 type="tel"
                 class="w-full"
-                placeholder="e.g. 0123456789"
+                placeholder="e.g. +60123456789"
               />
             </UFormField>
 
@@ -208,6 +208,7 @@
 import type { FormError, FormSubmitEvent } from '@nuxt/ui'
 
 import {
+  DEFAULT_PHONE_COUNTRY_CODE,
   hasValidFullName,
   isValidPhoneNumber,
   isValidUsername,
@@ -242,7 +243,7 @@ const editingUserId = ref<string | null>(null)
 const userForm = reactive({
   fullName: '',
   username: '',
-  phoneNumber: '',
+  phoneNumber: DEFAULT_PHONE_COUNTRY_CODE,
   role: 'staff' as UserRole
 })
 
@@ -287,7 +288,7 @@ await refreshUsers()
 function resetUserForm() {
   userForm.fullName = ''
   userForm.username = ''
-  userForm.phoneNumber = ''
+  userForm.phoneNumber = DEFAULT_PHONE_COUNTRY_CODE
   userForm.role = 'staff'
   editingUserId.value = null
 }
@@ -303,7 +304,7 @@ function openEditModal(user: ManagedUser) {
   editingUserId.value = user.id
   userForm.fullName = user.fullName
   userForm.username = user.username
-  userForm.phoneNumber = user.phoneNumber || ''
+  userForm.phoneNumber = user.phoneNumber ? normalizePhoneNumber(user.phoneNumber) : DEFAULT_PHONE_COUNTRY_CODE
   userForm.role = user.role
   editorOpen.value = true
 }
@@ -329,7 +330,7 @@ function validateUserForm(state: typeof userForm): FormError[] {
   }
 
   if (!isValidPhoneNumber(state.phoneNumber)) {
-    errors.push({ name: 'phoneNumber', message: 'Use a valid phone number with 8 to 15 digits.' })
+    errors.push({ name: 'phoneNumber', message: 'Use a valid phone number with country code, e.g. +60123456789.' })
   }
 
   return errors