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.local.yml

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