Make v0.1.0 Unraid-ready: multi-arch image, correct image path, registry-login docs

- Publish v0.1.0/latest as multi-arch (linux/amd64+arm64); amd64 passes 17/17 smoke
- publish-image.sh: add PLATFORMS multi-arch buildx mode (reproducible amd64 build)
- compose + unraid notes: fix image path to include jason/ namespace
- unraid notes: document required docker login (private package) and host label
  for docker build/push jobs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/publish-image.sh

@@ -25,6 +25,31 @@ LOCAL_TAG="${IMAGE_NAME}:${VERSION}"
 REMOTE_TAG="${REMOTE_REPO}:${VERSION}"
 REMOTE_LATEST="${REMOTE_REPO}:latest"
 
+# PLATFORMS (e.g. "linux/amd64,linux/arm64") triggers a multi-arch buildx build
+# that is pushed directly as a single manifest list. This is the recommended
+# path: Unraid hosts are amd64, so the published image must include amd64 even
+# when built on an arm64 (Apple Silicon) machine. Leave unset for a single-arch
+# tag-and-push of an already-built local image.
+PLATFORMS="${PLATFORMS:-}"
+
+if [ -n "${PLATFORMS}" ]; then
+    VCS_REF="$(git rev-parse --short HEAD 2>/dev/null || echo unknown)"
+    BUILD_DATE="$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+    echo "Building and pushing multi-arch (${PLATFORMS}) ${REMOTE_TAG} ..."
+    docker buildx build \
+        --platform "${PLATFORMS}" \
+        --build-arg "VERSION=${VERSION}" \
+        --build-arg "VCS_REF=${VCS_REF}" \
+        --build-arg "BUILD_DATE=${BUILD_DATE}" \
+        --tag "${REMOTE_TAG}" \
+        --tag "${REMOTE_LATEST}" \
+        --file docker/runner/Dockerfile \
+        --push \
+        .
+    echo "Published multi-arch: ${REMOTE_TAG} (${PLATFORMS})"
+    exit 0
+fi
+
 echo "Tagging ${LOCAL_TAG} as ${REMOTE_TAG} ..."
 docker tag "${LOCAL_TAG}" "${REMOTE_TAG}"
 docker tag "${LOCAL_TAG}" "${REMOTE_LATEST}"