feat(P1): Nova rebrand — docs/decks/prose/schema-$id/release-titles (REQ-155/156/157)

Rebrand ACDL/Agentic Cloud Delivery Platform → Nova across README, docs/,
decks (markdown + mermaid .mmd + HTML), pyproject.toml name/description,
schema $id URLs (acdl.cloudinit.dev→nova.cloudinit.dev), release.yml
title/workflow-name. Nova tagline added to README header + both deck title
slides + docs/vision.md (alongside existing North Star, D-106). S&P theme
untouched (D-107). New docs/NOVA_MIGRATION.md consumer guide. Data values
(env vars, resource names, tag keys, SSM/consumer paths) left for P2-P4.

---ci---
project: acdl
phase: 1
milestone: v1.15
status: execute
---/ci---

schemas/policy_check_result.schema.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://acdl.cloudinit.dev/schemas/policy_check_result.schema.json",
-  "title": "ACDL PolicyCheckResult",
+  "$id": "https://nova.cloudinit.dev/schemas/policy_check_result.schema.json",
+  "title": "Nova PolicyCheckResult",
   "description": "Normalized policy check result — the contract between policy engines and the confidence signal. Engine-specific adapters (checkov_adapter.py, future kyverno_adapter) translate native engine output to this shape. The confidence signal consumes a list of these as its policy input; it is engine-agnostic. The severity enum drives the severity->penalty mapping (critical hard-override, high -0.2, medium -0.05, low -0.01, info 0.0).",
   "$comment": "Canonical PolicyCheckResult (ARCHITECTURE.md §12.6). The confidence signal (platform/confidence_signal.py) consumes a list of these as its policy input; it is engine-agnostic. Adapters translate native output to this shape; the signal never reads engine-specific evidence.",
   "type": "object",