Initial commit: image registry structure and node-agent

Set up this repo as a base image registry. Each image is self-contained in
its own directory under images/ (Dockerfile + README.md + optional test.sh);
CI discovers them by glob, so adding an image needs no workflow changes.
template/ is the skeleton to copy.

The Makefile is the single entry point for both local work and CI, so a green
`make all` locally means a green pipeline.

Workflows:
  * lint.yaml  — layout check, hadolint, shellcheck
  * build.yaml — diffs against the base commit to build only the images that
    changed, smoke-tests each one before anything is published, then pushes.
    Releases are per-image tags (<image>/vX.Y.Z); main publishes :edge.

First image, node-agent: node:22-alpine plus a GNU userland (Alpine ships
BusyBox, whose applets take narrower flags than scripts and models expect),
helm, kubectl, jq, yq, bind-tools, curl, git, ripgrep, fd and friends.
Nothing is version-pinned — rebuilding is how upstream updates land, and the
published tag is what pins things for consumers.

Its smoke test asserts the deployment contract as well as tool presence: the
image must work non-root, with a read-only root filesystem and all
capabilities dropped, which is how ToolHive runs it.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

hack/select-images.sh

@@ -0,0 +1,96 @@
+#!/usr/bin/env bash
+# Decide which images CI should build. Prints GITHUB_OUTPUT lines:
+#
+#   images=["node-agent",...]   JSON array consumed by the build job's matrix
+#   any=true|false              whether there is anything to build at all
+#
+# Rules, first match wins:
+#   1. workflow_dispatch naming one image  -> that image
+#   2. tag push (<image>/vX.Y.Z)           -> the image named in the tag
+#   3. shared build plumbing changed       -> every image
+#   4. anything else                       -> images with changed files
+#
+# When the diff base is unknown (first push, force-push, shallow clone) this builds
+# everything. Rebuilding too much is the safe direction to fail.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+# A change to any of these can affect how every image is built.
+SHARED_PATHS='^(hack/|Makefile|\.hadolint\.yaml|\.gitea/workflows/)'
+
+all_images() {
+	local dockerfile
+	for dockerfile in images/*/Dockerfile; do
+		# Guards against the glob staying literal when there are no images.
+		[ -f "$dockerfile" ] || continue
+		basename "$(dirname "$dockerfile")"
+	done
+}
+
+# Names on stdin -> ["a","b"]. Built by hand so the runner needs no jq.
+as_json() {
+	local out='' name
+	while IFS= read -r name; do
+		[ -n "$name" ] || continue
+		out="${out:+$out,}\"$name\""
+	done
+	printf '[%s]' "$out"
+}
+
+emit() {
+	local names=$1 reason=$2 any=false
+	[ -n "$names" ] && any=true
+	echo "selected (${reason}): ${names:-<none>}" >&2
+	printf 'images=%s\n' "$(printf '%s\n' "$names" | as_json)"
+	printf 'any=%s\n' "$any"
+	exit 0
+}
+
+require_image() {
+	[ -f "images/$1/Dockerfile" ] || {
+		echo "no such image: images/$1/Dockerfile does not exist" >&2
+		exit 1
+	}
+}
+
+# 1. Explicit request via workflow_dispatch.
+case "${DISPATCH_IMAGE:-}" in
+	'') ;;
+	all) emit "$(all_images)" 'workflow_dispatch: all' ;;
+	*)
+		require_image "$DISPATCH_IMAGE"
+		emit "$DISPATCH_IMAGE" "workflow_dispatch: $DISPATCH_IMAGE"
+		;;
+esac
+
+# 2. Release tag: <image>/vX.Y.Z.
+if [ "${GITHUB_REF_TYPE:-}" = tag ]; then
+	image=${GITHUB_REF_NAME%/*}
+	require_image "$image"
+	emit "$image" "tag ${GITHUB_REF_NAME}"
+fi
+
+# 3 and 4 both need a usable diff base.
+base=${BASE_SHA:-}
+if [ -z "$base" ] || [[ $base =~ ^0+$ ]] || ! git cat-file -e "${base}^{commit}" 2>/dev/null; then
+	emit "$(all_images)" 'diff base unavailable, building everything'
+fi
+
+changed=$(git diff --name-only "$base" HEAD)
+
+if printf '%s\n' "$changed" | grep -qE "$SHARED_PATHS"; then
+	emit "$(all_images)" 'shared build plumbing changed'
+fi
+
+# Map changed paths back to image names, dropping any that no longer exist so a
+# deleted image directory does not fail the build.
+selected=$(
+	printf '%s\n' "$changed" |
+		sed -n 's#^images/\([^/]*\)/.*#\1#p' |
+		sort -u |
+		while IFS= read -r i; do
+			[ -f "images/$i/Dockerfile" ] && echo "$i"
+		done
+)
+
+emit "$selected" 'changed paths'