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/doctor.sh

@@ -0,0 +1,39 @@
+#shellcheck shell=sh
+# myos doctor  check that this installation can actually run a stack
+myos_cmd_doctor() {
+  _rc=0
+  _ok()   { printf '  %-28s %s\n' "$1" "$2"; }
+  _bad()  { printf '  %-28s %s%s%s\n' "$1" "$MYOS_C_ERROR" "$2" "$MYOS_C_RESET"; _rc=$MYOS_E_NOREQ; }
+
+  printf 'myos %s at %s\n' "$MYOS_VERSION" "$MYOS_ROOT"
+  printf 'requirements:\n'
+  if myos_have docker; then _ok docker "$(docker version --format '{{.Client.Version}}' 2>/dev/null || echo present)"
+  else _bad docker "not found"; fi
+  if _c=$(myos_compose_bin 2>/dev/null); then _ok "compose" "$_c"; else _bad compose "docker compose >= $MYOS_COMPOSE_MIN_VERSION not found"; fi
+  if [ "${DRYRUN:-false}" != true ]; then
+    if docker info >/dev/null 2>&1; then _ok "docker daemon" "reachable${DOCKER_HOST:+ via $DOCKER_HOST}"
+    else _bad "docker daemon" "unreachable${DOCKER_HOST:+ ($DOCKER_HOST)}"; fi
+  fi
+
+  printf 'configuration:\n'
+  for _f in $(myos_conf_files); do _ok "$_f" "read"; done
+  [ -f "$HOME/.config/myos/config" ] && _ok "$HOME/.config/myos/config" "read"
+  [ -f "$WORKDIR/.env" ] && _ok "$WORKDIR/.env" "read"
+  _ok ENV "$ENV"
+  _ok USER "$USER"
+  # shellcheck disable=SC3028  # HOSTNAME is set by bin/myos
+  _ok HOSTNAME "$HOSTNAME"
+  _ok DOMAIN "$DOMAIN"
+  _ok "project format" "${MYOS_PROJECT_FORMAT:-user-env-app}"
+
+  printf 'stacks:\n'
+  _p=$(myos_path)
+  if [ -n "$_p" ]; then printf '%s\n' "$_p" | tr ':' '\n' | sed 's/^/  /'
+  else _bad "stack path" "empty"; fi
+
+  # a .env written for the make engine can hold values the shell reads differently
+  if [ -f "$WORKDIR/.env" ] && grep -qE '\$\(|\$\{[a-z]' "$WORKDIR/.env"; then
+    printf '  %-28s %s%s%s\n' "$WORKDIR/.env" "$MYOS_C_WARN" "contains make expansions" "$MYOS_C_RESET"
+  fi
+  return "$_rc"
+}