Re-vendor carve-lib + section-wrap heading corpus fixtures

[dereuromark]

Completes the carve-side of the <section> wrapper rollout (PART 9 §13 spec landed in #18; carve-js renderer in markup-carve/carve-js#16).

What's in it

• docs/examples.md — the heading examples (Headings, Attributes, Heading IDs sections) rewritten from bare <h* id="…"> to the <section id="…"><h*>…</h*></section> shape, with the id on <section> and level-aware nesting.
• tests/corpus/*.html + tests/spec/*.test — regenerated via npm run corpus:build. 02-headings*, 17-attributes, and 19-heading-ids now carry the section-wrapped output.
• docs/.vitepress/carve-lib/ — re-vendored from carve-js main via npm run sync-carve-lib. Picks up the section-wrapping renderer plus the implicit-heading-reference resolution merged into carve-js since the last vendor.

Verification

86/86 corpus + normativity tests pass (npm test). The hand-written section HTML in examples.md was confirmed byte-identical against the re-vendored renderer (corpus test compares generated .html ← examples.md against carve-lib output).

Follow-up sequence

1. ✅ carve PR Spec: <section> wrapper around headings (P1.2) #18 — spec PART 9 §13
2. ✅ carve-js Adopt ASCII-safe heading id slugs (spec + corpus) #16 — renderer + tests (KNOWN_GAPS skip on the 6 heading fixtures)
3. (this PR) carve repo — re-vendor carve-lib + rewrite the heading fixtures
4. ⏳ carve-js — bump spec submodule + un-skip the 6 KNOWN_GAPS entries
5. ⏳ carve-php — implement the same section wrapping