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---

docs/presentations/assets/mmd/platform-architecture.mmd

@@ -7,7 +7,7 @@ flowchart TD
         U2["Citizen dev\nintent → AI agent → contract"]
     end
 
-    subgraph ACDL ["ACDL — infrastructure only"]
+    subgraph ACDL ["Nova — infrastructure only"]
         direction TB
         CS["Contract schema\n(validate + fail-fast)"]
         subgraph PIPE ["Central pipeline — fixed stages, every deployment"]