feat(P1): event emitters — CloudEvents envelope, Decision Ledger, Infracost adapter, attestation/confidence/policy event emission

P1 (Wave 1, feat) — REQ-187, REQ-188, REQ-205 (emitter), REQ-206 (emitter)

New components:
- core/metrics/event_envelope.py — CloudEvents 1.0 envelope + platform.* conventions
- core/metrics/run_manifest.py — per-run manifest writer (nova.run.started/completed/failed)
- core/metrics/decision_ledger.py — SQLite append-only hash-chain (ai.decision.made + attestation.recorded)
- core/metrics/infracost_adapter.py — Infracost post-processor (degraded mode when CLI absent, A6)
- schemas/metrics_event.schema.json — CloudEvents envelope schema
- schemas/metrics_run_manifest.schema.json — per-run manifest schema
- metrics/README.md — backup/restore doc (REQ-201)
- tests/test_metrics_emitters.py — 16 tests (all pass)

Modified components:
- core/confidence_signal.py — emits nova.confidence.computed + nova.ai.decision.made (D-122)
- core/hitl_gates.py — emits nova.attestation.recorded on qa/prod/dr gates (D-132)
- adapters/terraform/policy/checkov_adapter.py — emits nova.policy.evaluated
- pyproject.toml — addopts gains --junitxml + --json-report + --cov (REQ-206)
- .gitignore — metrics runtime artifacts ignored

D-120: Nova-native (JSONL + SQLite, no Kafka/OTel)
D-121: Decision Ledger = outbox_writer extension → SQLite hash-chain
D-122: AI decision = confidence_signal + HITL gate (not LLM)
D-128: metrics/ at repo root
D-132: Attestation instrumentation

---ci---
project: acdl
phase: 1
milestone: v1.17
status: execute
---/ci---

schemas/metrics_run_manifest.schema.json

@@ -0,0 +1,56 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Nova Per-Run Manifest",
+  "description": "Per-run manifest written to metrics/runs/<run_id>.json (REQ-187). Captures the full run lifecycle.",
+  "type": "object",
+  "required": ["run_id", "contract_id", "environment", "started_at", "completed_at", "exit_code", "stages"],
+  "properties": {
+    "run_id": {"type": "string", "minLength": 1},
+    "contract_id": {"type": "string"},
+    "environment": {"type": "string", "enum": ["dev", "qa", "prod", "dr"]},
+    "started_at": {"type": "string", "format": "date-time"},
+    "completed_at": {"type": "string", "format": "date-time"},
+    "exit_code": {"type": "integer"},
+    "stages": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "required": ["name", "duration_ms", "exit_code"],
+        "properties": {
+          "name": {"type": "string"},
+          "duration_ms": {"type": "number"},
+          "exit_code": {"type": "integer"},
+          "error": {"type": "string"}
+        }
+      }
+    },
+    "confidence": {
+      "type": "object",
+      "properties": {
+        "score": {"type": "number"},
+        "band": {"type": "string", "enum": ["pass", "warn", "block"]},
+        "perInput": {"type": "object"}
+      }
+    },
+    "hitl": {
+      "type": "object",
+      "properties": {
+        "gate": {"type": "string"},
+        "result": {"type": "string"},
+        "block": {"type": "boolean"}
+      }
+    },
+    "policy": {
+      "type": "object",
+      "properties": {
+        "passed": {"type": "integer"},
+        "failed": {"type": "integer"},
+        "skipped": {"type": "integer"}
+      }
+    },
+    "cost_estimate_usd": {"type": "number"},
+    "decision_id": {"type": "string"},
+    "outcome": {"type": "string", "enum": ["succeeded", "failed", "pending"]}
+  },
+  "additionalProperties": true
+}