Fix image workflow: vendor hub-core for legacy DinD docker (no buildx)

.forgejo/workflows/image.yaml

@@ -49,14 +49,20 @@ jobs:
               "https://forgejo.coulomb.social/${repo}/archive/${extra_ref}.tar.gz"
             mkdir -p "/tmp/ctx-${ctx}"
             tar xzf "/tmp/${ctx}.tar.gz" -C "/tmp/ctx-${ctx}" --strip-components=1
-            BUILD_ARGS+=(--build-context "${ctx}=/tmp/ctx-${ctx}")
           done
+          # Runner DinD has legacy docker (no buildx); vendor hub-core into context.
+          mkdir -p buildctx/_hub_core_src
+          cp -r /tmp/ctx-hub_core_src/pyproject.toml /tmp/ctx-hub_core_src/hub_core buildctx/_hub_core_src/
+          sed \
+            -e 's|COPY --from=hub_core_src pyproject.toml|COPY _hub_core_src/pyproject.toml|' \
+            -e 's|COPY --from=hub_core_src hub_core/|COPY _hub_core_src/hub_core/|' \
+            buildctx/Dockerfile > buildctx/Dockerfile.ci
           wget -qO- https://download.docker.com/linux/static/stable/x86_64/docker-27.3.1.tgz \
             | tar xz --strip-components=1 -C "${HOME}/bin" docker/docker
           export PATH="${HOME}/bin:${PATH}"
           echo "${REGISTRY_TOKEN}" | docker login "${REGISTRY}" -u "${REGISTRY_USER}" --password-stdin
           IMAGE="${REGISTRY}/${IMAGE_NAME}"
-          docker build "${BUILD_ARGS[@]}" \
+          docker build -f buildctx/Dockerfile.ci \
             -t "${IMAGE}:latest" -t "${IMAGE}:main-${SHORT}" buildctx
           docker push "${IMAGE}:latest"
           docker push "${IMAGE}:main-${SHORT}"