fix(P59): skip terraform validate test when terraform binary not installed

The test_s3_instance_emits_valid_terraform test runs terraform init+validate
as a subprocess. In CI, the ci.yml workflow doesn't install Terraform (only
the modules-lifecycle workflow does). The test now skips gracefully when
terraform is not on PATH, using shutil.which('terraform').

---ci---
project: acdl
phase: P59
milestone: v1.11
status: execute
---/ci---

tests/test_adapter.py

@@ -230,6 +230,9 @@ class TestAdapterEmitsValidTerraform:
     """The adapter-emitted root main.tf must pass terraform validate."""
 
     def test_s3_instance_emits_valid_terraform(self, tmp_path):
+        import shutil
+        if not shutil.which("terraform"):
+            pytest.skip("terraform binary not installed — run in a CI job with Terraform")
         instance = json.load(open(ROOT / "modules/l1/s3/instance.json"))
         adapt(instance, str(tmp_path))
         result = subprocess.run(