feat(P4): regression-gate policies + docs (REQ-304..307)

regression/ policies (3): cap-013-adapter-dedup, cap-023-metrics-collector,
cap-024-deck-structure — declarative mirrors of core/regression_verify.py
over capability-inventory JSON. The imperative regression_verify.py is kept
(drives CI gate); the policies are the declarative mirror (IDEATE I1 quality
improvement).

tests: test_regression_policies.py + clean/drifted fixtures. Skip-without-kj.

docs: adapters/README.md (new kyverno-json row + PolicyEngine Protocol
section with how-to-add-OpaEngine), adapters/kyverno-json/README.md (engine,
install, policy directory layout, 4 categories, severity convention),
schemas/README.md (D-116 engine enum reuse note), modules/STANDARDS.md §10
Policy Authoring Standard, docs/METRICS.md (swappable engine narrative).

---ci---
project: acdl
phase: 4
milestone: v1.25
status: execute
phase_role: execution
requirements:
  covered: [REQ-304, REQ-305, REQ-306, REQ-307]
  partial: []
---/ci---

adapters/kyverno-json/policies/regression/cap-024-deck-structure.json

@@ -0,0 +1,35 @@
+{
+  "apiVersion": "json.kyverno.io/v1alpha1",
+  "kind": "ValidatingPolicy",
+  "metadata": {
+    "name": "cap-024-deck-structure",
+    "annotations": {
+      "nova.cloudinit.dev/severity": "low",
+      "title.policy.kyverno.io": "Deck structure matches the documented 4-beat arc (CAP-024 declarative mirror)"
+    }
+  },
+  "spec": {
+    "rules": [
+      {
+        "name": "deck-has-4-beats",
+        "validate": {
+          "message": "The deck must have the 4-beat arc: Problem, Solution, Proof, Roadmap+Ask. Declarative mirror of core/regression_verify.py CAP-024.",
+          "assert": {
+            "all": [
+              {
+                "check": {
+                  "deck.beats": "(length(@) >= `4`)"
+                }
+              },
+              {
+                "check": {
+                  "deck.beats": "(contains(@, 'Problem') && contains(@, 'Solution') && contains(@, 'Proof') && contains(@, 'Roadmap+Ask'))"
+                }
+              }
+            ]
+          }
+        }
+      }
+    ]
+  }
+}