docs(P46): render Marp decks to HTML + PPTX, update README for rendered artifacts

Commit self-contained HTML renderings of both Marp presentation decks to
docs/presentations/ so they are viewable in any browser and on the git
forge. The HTML files embed all images as base64 data URIs and render
the full S&P Global Energy brand theme (#D6002A red-core, #1B1B1B grey-90,
Akkurat Pro font).

Updated the README to document the 3-step process with HTML as a
committed artifact (re-render when Marp source changes) and PPTX as a
Gitea release attachment (binary, not committed to git).

PPTX files are rendered and uploaded to the Gitea release as downloadable
attachments for stakeholders.

---ci---
phase: 46
milestone: v1.9
status: complete
requirements:
  covered: []
  partial: []
---/ci---

docs/presentations/README.md

@@ -63,9 +63,32 @@ Synthesize the full markdown into a lean Marp deck:
 - **Tighter prose** than Step 1 — strip the speaker-note nuance; keep the
   leadership-relevant selling points.
 
-### Step 3 — PPTX export
+### Step 3 — Render to HTML and PPTX
 
-Export the Marp deck to PPTX for stakeholders who want a slide file:
+Both formats are derived from the Marp deck. **HTML is committed to the repo**
+(viewable in any browser, self-contained with base64-embedded images). **PPTX
+is uploaded to the Gitea release** as a downloadable attachment (binary, not
+committed to git).
+
+#### HTML export (committed to repo)
+
+```bash
+CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
+  npx --yes @marp-team/marp-cli@latest --allow-local-files \
+  docs/presentations/<deck-name>-marp.md \
+  -o docs/presentations/<deck-name>.html
+```
+
+HTML export inlines images as base64 data URIs — no `--allow-local-files`
+needed for self-contained output, but it's required when the Marp deck
+references local PNG assets. The resulting HTML is a single self-contained
+file that renders the full deck with the S&P Global Energy theme.
+
+**Re-render the HTML whenever the Marp source changes.** The HTML files are
+committed artifacts, not generated on-the-fly — they must be re-rendered and
+re-committed when the Marp deck is updated.
+
+#### PPTX export (uploaded to Gitea release)
 
 ```bash
 CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
@@ -75,7 +98,9 @@ CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
 ```
 
 The `--allow-local-files` flag is **required** for PPTX export so the local
-PNG diagrams are embedded in the file.
+PNG diagrams are embedded in the file. PPTX files are not committed to the
+repo (binary, no meaningful diffs) — they are uploaded to the Gitea release
+as downloadable attachments.
 
 ## Directory layout
 
@@ -84,8 +109,10 @@ docs/presentations/
 ├── README.md                                  ← this file
 ├── how-the-platform-works.md                  ← Step 1: full source of truth
 ├── how-the-platform-works-marp.md              ← Step 2: Marp deck
+├── how-the-platform-works.html                  ← Step 3: rendered HTML (committed)
 ├── the-developer-experience.md                 ← Step 1: full source of truth
 ├── the-developer-experience-marp.md            ← Step 2: Marp deck
+├── the-developer-experience.html               ← Step 3: rendered HTML (committed)
 └── assets/
     ├── puppeteer-config.json                   ← no-sandbox config for mmdc
     ├── mmd/                                     ← mermaid source files (Step 2 input)
@@ -170,19 +197,23 @@ done
 The `puppeteer-config.json` passes `--no-sandbox` to the headless browser
 (required when running as root in this environment).
 
-### Export a Marp deck to HTML (for browser preview)
+### Export a Marp deck to HTML (committed to repo)
 
 ```bash
 CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
-  npx --yes @marp-team/marp-cli@latest \
+  npx --yes @marp-team/marp-cli@latest --allow-local-files \
   docs/presentations/<deck-name>-marp.md \
-  -o <output-path>.html
+  -o docs/presentations/<deck-name>.html
 ```
 
-HTML export inlines images as base64 data URIs — no `--allow-local-files`
-needed.
+HTML export inlines images as base64 data URIs. The `--allow-local-files`
+flag is needed when the Marp deck references local PNG assets (like the
+diagram images in `assets/png/`). The resulting HTML is self-contained.
 
-### Export a Marp deck to PPTX (for stakeholders)
+**The HTML files are committed artifacts** — re-render and re-commit whenever
+the Marp source changes.
+
+### Export a Marp deck to PPTX (uploaded to Gitea release)
 
 ```bash
 CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
@@ -192,7 +223,8 @@ CHROME_PATH=/root/.cache/ms-playwright/chromium-1217/chrome-linux64/chrome \
 ```
 
 `--allow-local-files` is **required** for PPTX so local PNG diagrams are
-embedded in the file.
+embedded in the file. PPTX files are not committed to git — upload them as
+attachments to the Gitea release.
 
 ## Adding a new presentation
 
@@ -203,8 +235,11 @@ embedded in the file.
    and render them to `assets/png/` (command above).
 3. **Synthesize the Marp deck** as `<deck-name>-marp.md` with frontmatter,
    no speaker notes, embedded PNGs, and maturity badges.
-4. **Export to PPTX** with `--allow-local-files`.
-5. **Verify** the PPTX slide count and that media files are embedded:
+4. **Render to HTML** with `--allow-local-files` and commit the HTML to
+   `docs/presentations/<deck-name>.html`.
+5. **Render to PPTX** with `--allow-local-files` and upload to the Gitea
+   release (do not commit PPTX to git).
+6. **Verify** the PPTX slide count and that media files are embedded:
    ```bash
    python3 -c "
    import zipfile, re
@@ -217,7 +252,7 @@ embedded in the file.
 
 ## Current decks
 
-| Deck | Source of truth (Step 1) | Marp deck (Step 2) | Audience |
-|---|---|---|---|
-| How the Platform Works | `how-the-platform-works.md` | `how-the-platform-works-marp.md` | CTO, Head of Cloud, Head of Infra, Head of DevOps |
-| The Developer Experience | `the-developer-experience.md` | `the-developer-experience-marp.md` | CTO, Head of Cloud, Head of Infra, Head of DevOps |
+| Deck | Source of truth (Step 1) | Marp deck (Step 2) | Rendered HTML (Step 3) | Audience |
+|---|---|---|---|---|
+| How the Platform Works | `how-the-platform-works.md` | `how-the-platform-works-marp.md` | `how-the-platform-works.html` | CTO, Head of Cloud, Head of Infra, Head of DevOps |
+| The Developer Experience | `the-developer-experience.md` | `the-developer-experience-marp.md` | `the-developer-experience.html` | CTO, Head of Cloud, Head of Infra, Head of DevOps |