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/ls.sh

@@ -0,0 +1,36 @@
+#shellcheck shell=sh
+# myos ls [--groups]  list the stacks myos can see, and where they come from
+myos_cmd_ls() {
+  case ${MYOS_REFS_RAW:-}${MYOS_ARGS:-} in
+    *--groups*) myos_ls_groups; return 0 ;;
+  esac
+  _IFS=$IFS; IFS=:
+  for _d in $(myos_path); do
+    IFS=$_IFS
+    printf '%s%s%s\n' "$MYOS_C_INFO" "$_d" "$MYOS_C_RESET"
+    for _s in "$_d"/*; do
+      [ -d "$_s" ] || continue
+      _n=$(basename "$_s")
+      _f=$(find "$_s" -maxdepth 1 \( -name '*.yml' -o -name '*.yaml' \) | wc -l | tr -d ' ')
+      [ "$_f" = 0 ] && continue
+      printf '  %-24s %s compose file(s)\n' "$_n" "$_f"
+    done
+    IFS=:
+  done
+  IFS=$_IFS
+}
+
+myos_ls_groups() {
+  _IFS=$IFS; IFS=:
+  for _d in $(myos_path); do
+    IFS=$_IFS
+    for _f in "$_d"/*.mk "$_d"/*.env "$_d"/*/*.mk; do
+      [ -f "$_f" ] || continue
+      _n=$(basename "$_f"); _n=${_n%.mk}; _n=${_n%.env}
+      _v=$(myos_group_value "$_n")
+      [ -n "$_v" ] && printf '%-16s %s\n' "$_n" "$_v"
+    done
+    IFS=:
+  done
+  IFS=$_IFS
+}