docs(milestone): complete v1.21 — Nova Deck Refinement & Pipeline Hardening

9 requirements complete (REQ-245..253):
- P1: strategic-docs — thesis rename + NORTH_STAR objectives + RACI
  restructure (REQ-246,247)
- P2: slides source-of-truth — rename + restructure + rewrite (REQ-245,
  248,249,252)
- P3: marp deck + talking points + README + theme CSS fix (REQ-251,252)
- P4: pipeline hardening — Checkov before plan, Wiz-or-Checkov on plan
  (REQ-250)
- P5: render + verify — new diagrams, HTML, PPTX, 686 tests pass (REQ-253)
- P6: final review + ship (this commit)

Deck renamed nova-no-humans-platform* -> nova-autonomous-cloud-delivery*.
Title: 'Nova — The Autonomous Cloud Delivery Platform'. 4-beat arc
(Problem -> Solution -> Proof -> Roadmap + Ask). 18 main + 1 appendix
slides. All 33 review notes applied. Tags on v1.20.x line (v1.20.0 P0 ->
v1.20.6 P6 final = milestone release).

---ci---
project: acdl
phase: 6
milestone: v1.21
status: complete
phase_role: final
requirements:
  covered: [REQ-245,REQ-246,REQ-247,REQ-248,REQ-249,REQ-250,REQ-251,REQ-252,REQ-253]
  partial: []
---/ci---

.ciagent/REQUIREMENTS.md

@@ -1707,12 +1707,12 @@ release; attach the PPTX.
 
 | REQ | Phase | Status |
 |-----|-------|--------|
-| REQ-245 | P2 | pending |
-| REQ-246 | P1 | pending |
-| REQ-247 | P1 | pending |
-| REQ-248 | P2 | pending |
-| REQ-249 | P2 | pending |
-| REQ-250 | P4 | pending |
-| REQ-251 | P3 | pending |
-| REQ-252 | P2 | pending |
-| REQ-253 | P5 | pending |
+| REQ-245 | P2 | complete |
+| REQ-246 | P1 | complete |
+| REQ-247 | P1 | complete |
+| REQ-248 | P2 | complete |
+| REQ-249 | P2 | complete |
+| REQ-250 | P4 | complete |
+| REQ-251 | P3 | complete |
+| REQ-252 | P2 | complete |
+| REQ-253 | P5 | complete |