generateDeck: not ported to v4 — evaluate modern slide tooling before porting

`generateDeck` is still a v3 `scripts/generateDeck.gradle` and was **not ported** to a v4 `.groovy` task.

Before investing in a v4 port, note that **slide-from-Markdown/AsciiDoc tooling has matured a lot**: asciidoctor-revealjs, [Marp](https://marp.app/), [Slidev](https://sli.dev/), reveal.js directly. A hand-maintained jBake/Gradle deck task may no longer be the best answer.

**Decision needed:**
- [ ] Port `generateDeck` to v4 as-is, **or**
- [ ] Recommend/integrate a modern tool and document the migration path, **or**
- [ ] Drop it.

For now: leave `generateDeck` unported; this issue tracks the decision. Related: v4 task rollout, DtcException.

Start by reading scripts/generateDeck.gradle and the related v4 task rollout mentioned in the issue. Compare the listed slide-from-Markdown/AsciiDoc tools and determine whether to port, replace, or drop the task; done means the decision and, if applicable, the migration path are documented.

Written by the indexing model from the issue text.