Install Docker in step 1; document registry login in step 2

- install-rubix.sh: apt install docker.io and compose plugin, enable daemon
- README: step 1 lists Docker install; step 2 keeps docker login before up.sh

install-rubix.sh

@@ -24,6 +24,7 @@ GITEA_TOKEN="${GITEA_TOKEN:-${GITEA_REGISTRY_PULL_TOKEN:-}}"
 TAG="${1:-}"
 
 APT_PACKAGES=(unzip wget curl python3 ca-certificates git rsync)
+DOCKER_PACKAGES=(docker.io docker-compose-plugin)
 
 prepare_system() {
   if [[ "$(id -u)" -ne 0 ]]; then
@@ -43,6 +44,22 @@ prepare_system() {
   fi
   echo "[install-rubix] apt-get install ${APT_PACKAGES[*]} ..."
   apt-get install -y "${APT_PACKAGES[@]}"
+  ensure_docker
+}
+
+ensure_docker() {
+  if command -v docker >/dev/null 2>&1; then
+    echo "[install-rubix] docker already installed: $(docker --version)"
+  else
+    echo "[install-rubix] apt-get install ${DOCKER_PACKAGES[*]} ..."
+    apt-get install -y "${DOCKER_PACKAGES[@]}"
+  fi
+  systemctl enable --now docker
+  if ! docker info >/dev/null 2>&1; then
+    echo "[install-rubix] ERROR: docker installed but daemon not running." >&2
+    exit 1
+  fi
+  echo "[install-rubix] docker OK ($(docker compose version 2>/dev/null | head -1 || docker --version))"
 }
 
 prompt_token() {
@@ -99,8 +116,9 @@ fi
 rm -f rubix.zip
 echo ""
 echo "[install-rubix] done — ${RUBIX_INSTALL_PATH} (${TAG})"
-echo "[install-rubix] next (see rubix README step 2):"
+echo "[install-rubix] next (see rubix-deploy README step 2):"
 echo "  cd ${RUBIX_INSTALL_PATH}/deploy/docker"
 echo "  cp .env.example .env"
-echo "  nano .env"
+echo "  nano .env   # set GITEA_REGISTRY_PULL_TOKEN, passwords, domains"
+echo "  # docker login before up.sh (see README step 2)"
 echo "  sudo ./up.sh"