add the myos CLI: one model for both modes

A stack is a directory of compose files; the current directory is a stack when
it holds one. The same command works for a project, a catalogue stack, a group
and a host singleton, and stacks sharing a project are now a single compose
call.

Two traps of the make engine are closed on the way: an unknown command is an
error instead of a silent success, and a group is only expanded when its name
is lowercase, so an environment variable can no longer be mistaken for one.
That guard spells out its character class because a-z matches uppercase too
under a dictionary collation.

lib/cmd/env.sh

@@ -0,0 +1,38 @@
+#shellcheck shell=sh
+# myos env [VAR...]  show resolved variables (replaces the make print-VAR target)
+myos_cmd_env() {
+  _vars=${MYOS_VARS:-}
+  [ -n "$_vars" ] || _vars=$MYOS_ARGS
+  [ -n "$_vars" ] || _vars=$MYOS_REFS_RAW
+  if [ -z "$_vars" ]; then
+    _vars="ENV USER HOSTNAME DOMAIN WORKDIR MYOS_PATH STACK COMPOSE_PROJECT_NAME COMPOSE_FILE"
+  fi
+  for _v in $_vars; do
+    case $_v in
+      MYOS_PATH)            printf '%s %s\n' "$_v" "$(myos_path)" ;;
+      COMPOSE_FILE)         printf '%s %s\n' "$_v" "$(myos_all_compose_files | tr '\n' ' ' | sed 's/ $//')" ;;
+      COMPOSE_PROJECT_NAME) printf '%s %s\n' "$_v" "$(myos_first_project)" ;;
+      STACK)                printf '%s %s\n' "$_v" "$(printf '%s' "$MYOS_STACKS" | tr '\n' ' ' | sed 's/ $//')" ;;
+      *)                    printf '%s %s\n' "$_v" "$(myos_var "$_v")" ;;
+    esac
+  done
+}
+
+# myos_all_compose_files  every compose file of every requested stack, in order
+myos_all_compose_files() {
+  for _ref in $MYOS_STACKS; do
+    myos_stack_compose_files "$_ref" 2>/dev/null
+  done
+  [ -f "$MYOS_ROOT/share/compose/networks.yml" ] && printf '%s\n' "$MYOS_ROOT/share/compose/networks.yml"
+  return 0
+}
+
+# myos_first_project  the compose project of the first requested stack
+myos_first_project() {
+  for _ref in $MYOS_STACKS; do
+    _app=$(myos_stack_name "$_ref")
+    case $_ref in .|./*|/*|../*) _app=$(basename "$(myos_stack_resolve "$_ref" 2>/dev/null)") ;; esac
+    myos_project_name "$(myos_scope "$_ref")" "$USER" "$ENV" "$_app"
+    return 0
+  done
+}