feat(emails): implement transactional email system with Resend

- Add Resend email integration with @react-email/render
- Create email templates: OrderConfirmation, OrderShipped, OrderCancelled, OrderPaid
- Implement webhook handler for ORDER_CREATED and other events
- Add multi-language support for customer emails
- Admin emails in English with order details
- Update checkout page with auto-scroll on order completion
- Configure DASHBOARD_URL environment variable

src/i18n/messages/en.json

@@ -391,6 +391,7 @@
     "emailRequired": "Required for order confirmation",
     "phoneRequired": "Required for delivery coordination",
     "shippingAddress": "Shipping Address",
+    "shippingMethod": "Shipping Method",
     "country": "Country",
     "firstName": "First Name",
     "lastName": "Last Name",
@@ -417,8 +418,11 @@
     "errorNoCheckout": "No active checkout. Please try again.",
     "errorEmailRequired": "Please enter a valid email address.",
     "errorFieldsRequired": "Please fill in all required fields.",
+    "errorNoShippingMethods": "No shipping methods available for this address. Please check your address or contact support.",
+    "errorSelectShipping": "Please select a shipping method.",
     "errorOccurred": "An error occurred during checkout.",
     "errorCreatingOrder": "Failed to create order.",
+    "continueToShipping": "Continue to Shipping",
     "orderConfirmed": "Order Confirmed!",
     "thankYou": "Thank you for your purchase.",
     "orderNumber": "Order Number",