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/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