Feature: Add WhatsApp notifications for collection-ready orders

- Implement WhatsApp Business API integration via Meta Cloud API
- Add phoneNumber field to Order model for storing customer phone numbers
- Update admin order detail page with phone number input for collection orders
- Send WhatsApp notification when admin marks order as ready for collection
- Add WhatsApp service module with phone number formatting and message sending
- Create database migrations for collection-related fields
- Add WhatsApp credentials to .env configuration

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

prisma/schema.prisma

@@ -231,6 +231,9 @@ model Order {
   carrier         String? @default("Royal Mail") // e.g. "Royal Mail", "DPD", "Courier"
   trackingNumber  String? // tracking number from carrier
   estimatedDeliveryDate DateTime? // estimated delivery date
+  collectedByCustomer Boolean @default(false) // true if order was collected by customer (no shipping)
+  isCollectionPickup Boolean @default(false) // true if customer selected collection at checkout
+  readyForCollection Boolean @default(false) // true when admin marks order as ready for pickup
 
   createdAt       DateTime    @default(now())
   updatedAt       DateTime    @updatedAt
@@ -240,6 +243,7 @@ model Order {
 
   guestName  String? // full name for guest orders
   guestPhone String? // contact phone for guest orders
+  phoneNumber String? // phone number for WhatsApp notifications (collection orders)
 
   items OrderItem[]
 }