docs(init): validate specification — v1.23 milestone (REQ-263..275)

Established active_milestone: v1.23 (Nova Deck Cleanup & Python PPTX).
NFR milestone (docs/render/test only; no features). Tags on v1.22.x line
(v1.22.0 P0 -> v1.22.6 P6 final = milestone release). Branch:
milestone/v1.23-deck-cleanup-python-pptx.

Added REQ-263..275 to REQUIREMENTS.md covering:
- Consolidate docs: single -marp.md source of truth, delete plain .md,
  speaker notes/talking points as Marp HTML comments, keep
  talking-points.md as synced standalone aid (REQ-263,264)
- Restore clean style: theme:default + inline style block (S&P palette),
  retire nova-sp-theme.css from render (keep as reference), benefit
  callout restyle (REQ-265,266,267)
- Inline images: scripts/inline_images.py for self-contained
  redistributable HTML (REQ-268)
- Python PPTX generator: scripts/render_pptx.py structured editable
  S&P-themed PPTX via python-pptx, both PPTX outputs produced + attached
  (REQ-269,270)
- Trim word count: targeted ~20-30% trim on verbose slides, remove
  'penetrate' term (REQ-271,272)
- CI/tests/README: workflows install python-pptx, tests updated,
  README rewritten (REQ-273,274,275)

Driven by user feedback: deck looked 'out of whack'; wanted to return to
the clean style of the old the-developer-experience.html. Investigation
revealed the 'clean' reference was itself MARP output (default theme +
inline style); the standalone nova-sp-theme.css approach was fragile.

---ci---
project: acdl
phase: 0
milestone: v1.23
status: specify
---/ci---

.ciagent/CHECKPOINT.json

@@ -1,28 +1,9 @@
 {
-  "phase": 6,
-  "stage": "complete",
-  "milestone": "v1.22",
-  "phase_role": "final",
+  "phase": 0,
+  "stage": "specify",
+  "milestone": "v1.23",
+  "phase_role": "pre_execution",
   "attempts": 0,
-  "updated_at": "2026-08-11T15:30:00Z",
-  "milestone_complete": true,
-  "tag": "v1.21.6",
-  "requirements": ["REQ-254","REQ-255","REQ-256","REQ-257","REQ-258","REQ-259","REQ-260","REQ-261","REQ-262"],
-  "release": {
-    "forge": "gitea",
-    "releases_created": true,
-    "release_ids": {
-      "v1.21.0": 621,
-      "v1.21.1": 622,
-      "v1.21.2": 623,
-      "v1.21.3": 624,
-      "v1.21.4": 625,
-      "v1.21.5": 626,
-      "v1.21.6": 627
-    },
-    "milestone_release_id": 627,
-    "pptx_asset_id": 98,
-    "pptx_download_url": "https://git.cloudinit.dev/attachments/fe691962-4f4e-4321-ab5d-c2bb8c3fd6ad"
-  },
-  "notes": "v1.22 milestone complete. Tag v1.21.6 (milestone release). Merged to main + pushed to origin. All 7 Gitea releases created (ids 621-627). PPTX attached to milestone release (asset id 98). All milestone branches deleted. 9 requirements complete (REQ-254..262). 32 slide tests pass (23 original + 9 new). 94 key-file tests pass. Pipeline check exit 0. Next milestone starts fresh."
+  "updated_at": "2026-08-11T23:30:00Z",
+  "project": "acdl"
 }