ci: upload kustomize build artifacts

- Add upload-artifact step to preserve built kustomize YAML files
- Artifact naming includes PR number (or 'main' for push) and run ID
- Set retention to 30 days for PR workflow

Made-with: opencode
Model: big-pickle (opencode/big-pickle)

Author: cjeanner

.github/workflows/kustomize-build.yml

@@ -2,6 +2,7 @@
 name: kustomize-build
 permissions:
   contents: read
+  pull-requests: write
 on:  # yamllint disable-line rule:truthy
   pull_request:
     branches:
@@ -42,3 +43,10 @@ jobs:
 
       - name: Verify Kustomize builds
         run: python .github/scripts/verify-kustomize-builds.py
+
+      - name: Upload built artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: kustomize-${{ github.event.pull_request.number || 'main' }}-${{ github.run_id }}
+          path: .build-test/
+          retention-days: 30