fix(ci): fall back to ci-base:latest when ci-base:dev doesn't exist yet

The BASE build arg was hardcoded to ci-base:dev even when the pull fell
back to :latest. Docker then tried to resolve ci-base:dev from the
registry during the build and failed.

Capture which tag was actually pulled and use that as BASE.

.gitea/workflows/ci-dev.yaml

@@ -272,8 +272,9 @@ jobs:
           gcloud config set project neuron-785695
           gcloud auth configure-docker us-central1-docker.pkg.dev --quiet
 
-          # Pull existing ci-base:dev (system deps stay cached in the base layer)
-          docker pull "${CI_BASE}:dev" || docker pull "${CI_BASE}:latest"
+          # Pull existing ci-base:dev (or fall back to :latest on first run)
+          BASE_TAG="dev"
+          docker pull "${CI_BASE}:dev" || { docker pull "${CI_BASE}:latest" && BASE_TAG="latest"; }
 
           # Inline Dockerfile — only replaces the El SDK layer
           cat > /tmp/Dockerfile.ci-base-patch << 'EOF'
@@ -288,7 +289,7 @@ jobs:
           EOF
 
           docker build \
-            --build-arg BASE="${CI_BASE}:dev" \
+            --build-arg BASE="${CI_BASE}:${BASE_TAG}" \
             --build-arg BUILDKIT_INLINE_CACHE=1 \
             -f /tmp/Dockerfile.ci-base-patch \
             -t "${CI_BASE}:dev" \