fix(P2): render scripts — delete render_deck.sh, pin versions, 2x scale (REQ-257,258)

REQ-257: deleted scripts/render_deck.sh (omitted --theme, produced
unthemed output; README already documents render_slides.sh as
canonical). Pinned marp-cli@4.5.0 + mermaid-cli@11.16.0 in
render_slides.sh to prevent boilerplate-CSS drift. Removed
render_deck.sh references from README, sync_to_nova.sh, and
test_no_forge_mentions.py.
REQ-258: added -s 2 -b transparent to mermaid-cli invocation (matches
README spec line 193). Produces crisp 2x PNGs with transparent
backgrounds instead of 1x renders.

---ci---
project: acdl
phase: 2
milestone: v1.22
status: execute
phase_role: execution
---/ci---

docs/presentations/README.md

@@ -84,8 +84,7 @@ CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
 
 HTML export inlines images as base64 data URIs. PPTX export requires
 `--allow-local-files` so the local PNG diagrams are embedded in the file.
-The render + commit + attach pipeline is automated by `scripts/render_deck.sh`
-and `scripts/render_slides.sh`.
+The render + commit + attach pipeline is automated by `scripts/render_slides.sh`.
 
 ### Step 4 — Talking points (presenter cues)