test(P5): ci + tests + readme for single-doc dual-pptx pipeline (REQ-273,274,275)

CI workflows: install python-pptx, pin CLI versions, stage both PPTX +
inlined HTML. test_slides_pipeline.py: inverted theme assertion (now
default+inline), deleted source-md tests, added 8 new tests
(penetrate absence, image inlining, python-pptx, benefit class, single
source, speaker-notes comments, default theme, css retained). New
test_pptx_generator.py: slide count, title colors, slide titles, table
rendering, image embedding, benefit callout. README rewritten for 3-step
single-document + dual-PPTX + image-inlining pipeline.

---ci---
project: acdl
phase: 5
milestone: v1.23
status: execute
phase_role: execution
---/ci---

.github/workflows/slides.yml

@@ -1,11 +1,15 @@
 # Nova Slides Render — re-renders presentation deck when source files change.
+# REQ-273: install python-pptx, pin CLI versions, stage HTML + both PPTX +
+# base64-inlined images.
 name: Nova Slides Render
 on:
   push:
     paths:
       - 'docs/presentations/**'
       - 'scripts/render_slides.sh'
-      - 'assets/nova-sp-theme.css'
+      - 'scripts/inline_images.py'
+      - 'scripts/render_pptx.py'
+      - 'pyproject.toml'
   workflow_dispatch:
 
 jobs:
@@ -16,16 +20,24 @@ jobs:
         with: { fetch-depth: 0 }
       - uses: actions/setup-node@v4
         with: { node-version: '20' }
-      - name: Install Chrome
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+      - name: Install python-pptx (slides extra)
+        run: pip install -e ".[slides]"
+      - name: Install + pin render CLIs
         run: |
-          npx --yes @marp-team/marp-cli@latest --version
-          npx --yes @mermaid-js/mermaid-cli --version
+          npx --yes @marp-team/marp-cli@4.5.0 --version
+          npx --yes @mermaid-js/mermaid-cli@11.16.0 --version
       - name: Render slides
         run: bash scripts/render_slides.sh
       - name: Commit rendered artifacts
         run: |
           git config user.name "nova-slides-bot"
           git config user.email "bot@nova.local"
-          git add docs/presentations/*.html docs/presentations/*.pptx docs/presentations/assets/png/*.png
+          git add docs/presentations/*.html \
+                  docs/presentations/*.pptx \
+                  docs/presentations/*-python.pptx \
+                  docs/presentations/assets/png/*.png
           git diff --cached --quiet || git commit -m "chore(slides): re-render deck [skip ci]"
-          git push
+          git push