ci(bluebuild): login to GHCR with PAT, share auth.json into bluebuild

GHCR rate-limited anonymous pulls (403 on bearer token). Login with
the GHCR_PULL_TOKEN secret (s8n-ru read-only PAT), then bind-mount
podman's auth.json into the bluebuild CLI container so its inner
buildah sees the same login.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/build-bluebuild.yml

@@ -96,13 +96,21 @@ jobs:
           cosign version
 
       - name: Pre-pull secureblue base image
+        env:
+          GHCR_PULL_TOKEN: ${{ secrets.GHCR_PULL_TOKEN }}
         run: |
           set -euxo pipefail
-          # GHCR's manifest API rejects anonymous calls from skopeo
-          # ("Not authorized") for some public images — but `podman
-          # pull` handles the anonymous token dance correctly. Pre-pull
-          # the base into local podman storage so bluebuild's
-          # templating step finds it without a registry round-trip.
+          # GHCR rate-limits anonymous CI pulls (403 on bearer-token).
+          # Login with a read-only PAT (forgejo secret GHCR_PULL_TOKEN)
+          # so bluebuild's buildah inside the CLI container also sees a
+          # valid auth.json via shared storage bind-mount below.
+          if [ -n "${GHCR_PULL_TOKEN:-}" ]; then
+            echo "$GHCR_PULL_TOKEN" | podman login \
+              --username s8n-ru \
+              --password-stdin ghcr.io
+          else
+            echo "[WARN] GHCR_PULL_TOKEN secret empty; trying anonymous pull"
+          fi
           podman pull ghcr.io/secureblue/securecore-kinoite-hardened-userns:latest
 
       - name: Build OCI image with BlueBuild CLI container
@@ -120,11 +128,18 @@ jobs:
           # CLI container so buildah inside it can see the pre-pulled
           # secureblue base layer (avoids GHCR auth round-trip during
           # templating).
+          # Mount podman's auth.json so the bluebuild container can
+          # authenticate to GHCR via the same login we did above.
+          AUTH_JSON="${XDG_RUNTIME_DIR:-/run/containers/0}/containers/auth.json"
+          [ -f "$AUTH_JSON" ] || AUTH_JSON=/root/.config/containers/auth.json
+          ls -la "$AUTH_JSON" 2>&1 || true
+
           podman run --rm \
             --privileged \
             --entrypoint /usr/bin/bluebuild \
             -v "$PWD:/work" \
             -v /var/lib/containers/storage:/var/lib/containers/storage \
+            -v "${AUTH_JSON}:/root/.config/containers/auth.json:ro" \
             -w /work \
             -e BB_BUILD_DRIVER=buildah \
             ghcr.io/blue-build/cli:latest \