Add headless Angor services and shared-index install guard

apps/angor-indexer/container/entrypoint.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -eu
+# Resolve through the container runtime's DNS, including after dependency
+# recreation. Never bake a container IP into the indexer endpoint.
+DNS_RESOLVER=$(awk '/^nameserver[[:space:]]/ {print $2; exit}' /etc/resolv.conf)
+case "$DNS_RESOLVER" in
+  ''|*[!0-9a-fA-F.:]*) echo 'Container DNS resolver is unavailable' >&2; exit 1 ;;
+esac
+case "$DNS_RESOLVER" in *:*) DNS_RESOLVER="[$DNS_RESOLVER]" ;; esac
+export DNS_RESOLVER
+envsubst '${DNS_RESOLVER}' < /etc/angor-nginx.conf.template > /tmp/nginx.conf
+exec nginx -c /tmp/nginx.conf -g 'daemon off;'