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/workflows/manage-example-branches.yml

@@ -0,0 +1,25 @@
+# Branches with names starting with `example` are meant to be long living branches used as
+# documentation/usage example.
+# After accepting the branch, the main PR should be closed
+name: Example branch management
+
+on: pull_request
+
+jobs:
+  example-branches-checks:
+    if: ${{ startsWith(github.head_ref, 'example') }}
+    name: Checks
+    runs-on: ubuntu-22.04
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions-ecosystem/action-add-labels@bd52874380e3909a1ac983768df6976535ece7f8 # v1.1.0
+        name: Set example label
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          labels: |
+            example
+      - name: Example branches are not meant to be merged
+        run: |
+          echo "Example branches are not meant to be merged"
+          exit 1