feat: complete saleor core extensions app with React email templates

- Order confirmation, shipped, and cancelled email templates
- Uses @react-email/components for professional HTML emails
- Sends admin and customer notifications
- Integrates with Resend for email delivery
- Webhook handlers for ORDER_CREATED, ORDER_FULFILLED, ORDER_CANCELLED
- Docker image optimized for production
- Persistent auth data storage via PVC

graphql/subscriptions/order-cancelled.graphql

@@ -0,0 +1,5 @@
+subscription OrderCancelledSubscription {
+  event {
+    ...OrderCancelledWebhookPayload
+  }
+}

graphql/subscriptions/order-created.graphql

@@ -0,0 +1,5 @@
+subscription OrderCreatedSubscription {
+  event {
+    ...OrderCreatedWebhookPayload
+  }
+}

graphql/subscriptions/order-filter-shipping-methods.graphql

@@ -0,0 +1,5 @@
+subscription OrderFilterShippingMethodsSubscription {
+  event {
+    ...OrderFilterShippingMethodsPayload
+  }
+}

graphql/subscriptions/order-fulfilled.graphql

@@ -0,0 +1,5 @@
+subscription OrderFulfilledSubscription {
+  event {
+    ...OrderFulfilledWebhookPayload
+  }
+}