ci: use default docker builder instead of creating new one

docker driver only supports a single instance. Creating another fails with
'additional instances of driver docker cannot be created'. Just use the
default builder that ships with the docker daemon.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Jenkinsfile

@@ -74,15 +74,11 @@ pipeline {
                     # Verify emulation works before proceeding
                     sudo docker run --rm --platform linux/arm64 docker.m.daocloud.io/library/alpine:latest uname -m
 
-                    # Use the default docker driver (not docker-container) so buildkit
-                    # runs inside the host daemon — no separate moby/buildkit container
-                    # needs to be pulled from Docker Hub.
-                    sudo docker buildx rm ${BUILDER_NAME} >/dev/null 2>&1 || true
-                    sudo docker buildx create \
-                      --name ${BUILDER_NAME} \
-                      --driver docker \
-                      --use
-                    sudo docker buildx inspect --builder ${BUILDER_NAME} --bootstrap >/dev/null
+                    # Use the default docker builder (docker driver) — not a separate
+                    # docker-container instance — so we don't need to pull moby/buildkit
+                    # from unreachable Docker Hub.
+                    sudo docker buildx use default 2>/dev/null || true
+                    sudo docker buildx inspect --bootstrap >/dev/null
                 """
             }
         }