feat(P2): dedicated S&P theme + render pipeline + CI workflow (REQ-239..243)

Create nova-sp-theme.css — S&P Global Energy Marp theme (Red/Black/White
palette applied to all slide chrome: backgrounds, headers/footers, pagination,
tables, blockquotes, code blocks).
Create render_slides.sh — end-to-end pipeline: mermaid PNGs + Marp HTML/PPTX.
Create slides.yml CI workflow — auto-renders on docs/presentations/ changes.
Create test_slides_pipeline.py — 12 tests (theme CSS, Marp frontmatter, script,
workflow, .mmd/.png parity, README retired-deck cleanup).
Update Marp frontmatter: theme: nova-sp + footer v1.20.
Fix presentations/README.md directory layout (remove retired decks).
Re-render HTML + PPTX with S&P theme.

---ci---
project: acdl
phase: 2
milestone: v1.20
status: execute
requirements: [REQ-239, REQ-240, REQ-241, REQ-242, REQ-243]
---/ci---

tests/test_slides_pipeline.py

@@ -0,0 +1,126 @@
+"""REQ-239..243 (v1.20): S&P theme + slide render pipeline tests.
+
+Validates:
+  - The Marp deck frontmatter references nova-sp-theme.css
+  - The CSS file contains the S&P colors (#D6002A, #1B1B1B)
+  - The mermaid theme JSON contains the S&P colors
+  - Every .mmd has a corresponding .png
+  - The render_slides.sh script exists and is executable
+  - The CI workflow file exists
+"""
+import re
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+PRESENTATIONS = ROOT / "docs" / "presentations"
+ASSETS = PRESENTATIONS / "assets"
+THEME_CSS = ASSETS / "nova-sp-theme.css"
+THEME_JSON = ASSETS / "mmd" / "sp-theme.json"
+MARP_DECK = PRESENTATIONS / "nova-no-humans-platform-marp.md"
+RENDER_SCRIPT = ROOT / "scripts" / "render_slides.sh"
+SLIDES_WORKFLOW = ROOT / ".github" / "workflows" / "slides.yml"
+
+
+def test_sp_theme_css_exists():
+    """REQ-239: nova-sp-theme.css exists."""
+    assert THEME_CSS.is_file(), f"theme CSS not found: {THEME_CSS}"
+
+
+def test_sp_theme_css_has_snp_colors():
+    """REQ-239: CSS contains S&P Red and Black."""
+    css = THEME_CSS.read_text()
+    assert "#D6002A" in css, "S&P Red (#D6002A) missing from theme CSS"
+    assert "#1B1B1B" in css, "S&P Black (#1B1B1B) missing from theme CSS"
+
+
+def test_sp_theme_json_has_snp_colors():
+    """The mermaid theme JSON also has S&P colors."""
+    json_text = THEME_JSON.read_text()
+    assert "#D6002A" in json_text, "S&P Red missing from mermaid theme"
+    assert "#1B1B1B" in json_text, "S&P Black missing from mermaid theme"
+
+
+def test_marp_deck_uses_sp_theme():
+    """REQ-239: Marp deck frontmatter references nova-sp-theme.css."""
+    text = MARP_DECK.read_text()
+    # The frontmatter is between the first two ---
+    fm_match = re.match(r'^---\n(.*?)\n---', text, re.DOTALL)
+    assert fm_match, "Marp frontmatter not found"
+    frontmatter = fm_match.group(1)
+    assert "nova-sp" in frontmatter, \
+        "Marp deck does not reference nova-sp theme"
+
+
+def test_marp_deck_not_using_default_theme():
+    """The Marp deck must not use 'theme: default'."""
+    text = MARP_DECK.read_text()
+    fm_match = re.match(r'^---\n(.*?)\n---', text, re.DOTALL)
+    assert fm_match, "Marp frontmatter not found"
+    frontmatter = fm_match.group(1)
+    assert "theme: default" not in frontmatter, \
+        "Marp deck still uses 'theme: default' — should use nova-sp-theme.css"
+
+
+def test_render_slides_script_exists():
+    """REQ-240: render_slides.sh exists and is executable."""
+    assert RENDER_SCRIPT.is_file(), "render_slides.sh not found"
+    import os
+    assert os.access(RENDER_SCRIPT, os.X_OK), "render_slides.sh not executable"
+
+
+def test_render_slides_script_renders_mermaid():
+    """REQ-240: render_slides.sh renders mermaid diagrams."""
+    text = RENDER_SCRIPT.read_text()
+    assert "mermaid-cli" in text or "mmdc" in text, \
+        "render_slides.sh does not invoke mermaid-cli"
+    assert "sp-theme.json" in text, \
+        "render_slides.sh does not reference sp-theme.json"
+
+
+def test_render_slides_script_renders_marp():
+    """REQ-240: render_slides.sh renders Marp HTML + PPTX."""
+    text = RENDER_SCRIPT.read_text()
+    assert "marp-cli" in text, "render_slides.sh does not invoke marp-cli"
+    assert ".html" in text, "render_slides.sh does not produce HTML"
+    assert ".pptx" in text, "render_slides.sh does not produce PPTX"
+
+
+def test_slides_ci_workflow_exists():
+    """REQ-241: CI workflow for slides exists."""
+    assert SLIDES_WORKFLOW.is_file(), "slides.yml workflow not found"
+
+
+def test_slides_ci_workflow_triggers_on_presentations():
+    """REQ-241: CI workflow triggers on docs/presentations/ changes."""
+    text = SLIDES_WORKFLOW.read_text()
+    assert "docs/presentations" in text, \
+        "slides.yml does not trigger on docs/presentations/"
+    assert "render_slides.sh" in text, \
+        "slides.yml does not invoke render_slides.sh"
+
+
+def test_every_mmd_has_png():
+    """REQ-240: every .mmd file has a corresponding .png."""
+    mmd_dir = ASSETS / "mmd"
+    png_dir = ASSETS / "png"
+    if not mmd_dir.is_dir():
+        pytest.skip("no .mmd directory")
+    mmd_files = sorted(mmd_dir.glob("*.mmd"))
+    assert len(mmd_files) > 0, "no .mmd files found"
+    missing = []
+    for mmd in mmd_files:
+        png = png_dir / f"{mmd.stem}.png"
+        if not png.is_file():
+            missing.append(mmd.name)
+    assert not missing, f"PNGs missing for: {missing}"
+
+
+def test_readme_no_retired_decks():
+    """REQ-243: presentations README does not list retired decks."""
+    readme = (PRESENTATIONS / "README.md").read_text()
+    assert "how-the-platform-works" not in readme, \
+        "README still references retired 'how-the-platform-works' deck"
+    assert "the-developer-experience" not in readme, \
+        "README still references retired 'the-developer-experience' deck"