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_tasks_validation.py

@@ -302,7 +302,13 @@ class AckTaskValidationTests(unittest.TestCase):
             with self.subTest(invalid_semver=invalid):
                 self.assertIsNone(ack_pattern.fullmatch(invalid))
 
-        current_gate, orchestration_gate, receipts_gate, delivery_gate = schema["allOf"]
+        (
+            current_gate,
+            orchestration_gate,
+            receipts_gate,
+            delivery_gate,
+            regression_gate,
+        ) = schema["allOf"]
         current_pattern = re.compile(
             current_gate["if"]["properties"]["ackVersion"]["pattern"]
         )
@@ -341,6 +347,7 @@ class AckTaskValidationTests(unittest.TestCase):
                 "#/definitions/launchableTasks",
             )
         self.assertIn("deliveryRuns", delivery_gate["then"]["required"])
+        self.assertIn("regressionRuns", regression_gate["then"]["required"])
 
         delivery_run = schema["definitions"]["deliveryRun"]
         revision_gate = delivery_run["allOf"][0]