fix(scripts): publish.sh — drop bogus auth check, helpful buildx error

- The 'authenticate first' reminder was checking docker system info's
  IndexServerAddress for 'gitea.04080616.xyz', but that field always
  reports Docker Hub regardless of which registries you've logged into.
  The reminder fired even right after a successful 'docker login' to
  Gitea — pure noise. Reduced to a comment for the maintainer.

- The buildx error message now points at the actual root cause: buildx
  is usually installed at the per-user ~/.docker/cli-plugins path, which
  sudo doesn't see. Two fixes presented: docker group (no-sudo) or apt
  install docker-buildx-plugin (sudo).

scripts/publish.sh

@@ -51,23 +51,37 @@ EOF
   exit 1
 fi
 
-if ! "${DOCKER[@]}" system info --format '{{json .IndexServerAddress}}' 2>/dev/null | grep -q "gitea.04080616.xyz"; then
-  cat <<EOF >&2
-Reminder: authenticate first as the same user that runs the build:
-  ${SUDO:+sudo }docker login gitea.04080616.xyz
-EOF
-fi
+# (Earlier versions checked `docker system info` for the registry — but
+# IndexServerAddress always points at Docker Hub regardless of which
+# registries you've logged into, so the check was a guaranteed false
+# positive. If push fails with 401, run:
+#   ${SUDO:+sudo }docker login gitea.04080616.xyz
 
 IMAGE_TAG="${1:-${DOCKER_IMAGE_TAG:-latest}}"
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 PLATFORMS="${CM_IMAGE_PLATFORMS:-linux/amd64}"
 
 if ! "${DOCKER[@]}" buildx version >/dev/null 2>&1; then
-  cat <<'EOF' >&2
-Docker Buildx is required for producing registry-compatible images.
-Install/enable buildx and rerun, for example:
-  docker buildx create --use --name cm-bot-builder
-  docker buildx inspect --bootstrap
+  cat <<EOF >&2
+Docker Buildx isn't reachable as the user this script runs docker as
+(${SUDO:+root via sudo}${SUDO:-current user}).
+
+Likely cause: buildx is installed at the per-user path
+~/.docker/cli-plugins/docker-buildx, which sudo doesn't see.
+
+Pick one fix:
+
+  1) Add yourself to the docker group (works for everything, no sudo):
+       sudo usermod -aG docker \$USER
+       newgrp docker
+       docker login gitea.04080616.xyz
+       NO_SUDO=1 bash scripts/publish.sh ${1:-latest}
+
+  2) Install the buildx plugin system-wide:
+       sudo apt install docker-buildx-plugin
+       sudo docker login gitea.04080616.xyz
+       bash scripts/publish.sh ${1:-latest}
+
 EOF
   exit 1
 fi