add shellspec golden harness for the legacy make engine

- spec/golden/cases.txt: 69 black-box cases (CLI wrapper mode and make
  include mode) run in a hermetic sandbox with a mocked docker
- spec/golden/expected/*.txt recorded from this engine (baseline)
- make test / test-golden / golden-record / lint dev targets

spec/fixtures/app-git/.env.dist

@@ -0,0 +1,2 @@
+APP_SERVICE_8080_TAGS=urlprefix-app.${DOMAIN}/*
+POSTGRES_PASSWORD=changeme

spec/fixtures/app-git/Makefile

@@ -0,0 +1,2 @@
+MYOS ?= /usr/local/lib/myos
+-include $(MYOS)/make/include.mk

spec/fixtures/app-git/docker-compose.local.yml

@@ -0,0 +1,4 @@
+services:
+  app:
+    environment:
+      DEBUG: "true"

spec/fixtures/app-git/docker-compose.yml

@@ -0,0 +1,13 @@
+services:
+  app:
+    image: alpine:3.20
+    command: sleep infinity
+    environment:
+      APP_DOMAIN: ${APP_DOMAIN}
+      DOMAIN: ${DOMAIN}
+    labels:
+      - SERVICE_8080_NAME=${COMPOSE_SERVICE_NAME}-app-8080
+      - SERVICE_8080_TAGS=${APP_SERVICE_8080_TAGS:-urlprefix-app.localhost/*}
+    networks:
+      - default
+      - private

spec/fixtures/app-git/docker/docker-compose.yml

@@ -0,0 +1,5 @@
+services:
+  db:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}