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

.github/copilot-instructions.md

@@ -0,0 +1,13 @@
+# Copilot Instructions
+
+## Verify Schema
+
+Whenever the user is asking for integration with Saleor API, verify the [schema.graphql](../graphql/schema.graphql) to match the queries, mutations and inputs required by Saleor API.
+
+## GraphQL Files
+
+Whenever the user requires some GraphQL query/mutation, write them to a .graphql file in [/graphql](../graphql) folder. Queries go to "/query", mutations go to "/mutations" etc.
+
+## Generating Types
+
+When you add a new GraphQL file, make sure to regenerate the types using the "generate" command from [package.json](../package.json). It may take some time for the TS Server to detect the changes.