feat(ack): bind test env to deployer and add regression mode

ACK 0.19.0 hands test-environment deploys to the deployer skill,
documents bug-fix as a first-class scenario, and adds
docs/ack/regression.yaml harvest plus a /ack regression run.

tests/test_ack_yaml_fallback.py

@@ -31,12 +31,14 @@ paths = (
     Path('skills/ack/examples/knowledge.example.yaml'),
     Path('skills/ack/templates/delivery.template.yaml'),
     Path('skills/ack/examples/delivery.example.yaml'),
+    Path('skills/ack/templates/regression.template.yaml'),
+    Path('skills/ack/examples/regression.example.yaml'),
 )
 for path in paths:
     value = load_yaml_subset(path.read_text(encoding='utf-8'))
     if not isinstance(value, dict):
         raise SystemExit(f'{path}: top-level value is not a mapping')
-print('parsed=6')
+print('parsed=8')
 """
         result = subprocess.run(
             [sys.executable, "-S", "-c", script],
@@ -47,7 +49,7 @@ print('parsed=6')
         )
 
         self.assertEqual(result.returncode, 0, result.stderr)
-        self.assertEqual(result.stdout.strip(), "parsed=6")
+        self.assertEqual(result.stdout.strip(), "parsed=8")
 
     def test_tasks_validator_runs_without_site_packages(self) -> None:
         result = subprocess.run(