fix: add explicit GHCR login for feature publish

The devcontainers/action OCI client doesn't always handle GHCR
authentication via GITHUB_TOKEN alone. Adding docker/login-action
ensures credentials are available.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: bradleybeddoes

.github/workflows/publish-feature.yml

@@ -14,6 +14,13 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Publish to GHCR
         uses: devcontainers/action@v1
         with: