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/stack.schema.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
-  "$id": "https://acdl.cloudinit.dev/schemas/stack.schema.json",
-  "title": "ACDL Target Stack",
+  "$id": "https://nova.cloudinit.dev/schemas/stack.schema.json",
+  "title": "Nova Target Stack",
   "description": "Angine-neutral description of a target stack: resources with typed inputs/outputs/NFRs, relationships (single parent per child), composition tree (max depth 5), and policy hooks. The L1 registry, L2 composition tree, contract YML, and PolicyCheckResult schema are all defined against this stack schema. Angine adapters (the Terraform adapter in v1) are the only engine-specific code.",
   "$comment": "v1 ships one adapter (Terraform). The stack is nearly isomorphic to Terraform in v1 (ARCHITECTURE.md §12.1); the adapter compiles resource.module -> module block, resource.inputs -> variable + arg, resource.outputs -> output, relationship.kind=uses_output -> interpolation, relationship.kind=parent -> composition ordering hint. As more adapters appear (v2+), the stack gains expressiveness; the L1 content + contract YML + composition tree do not change. The schema body is engine-agnostic: no Terraform block keywords (variable/output/resource as blocks) and no aws_ provider prefixes in the schema keywords; type values are stack types (aws:s3:bucket), not Terraform resource types (aws_s3_bucket).",
   "type": "object",