feat(spacecraft-standard): sync §8 Documentation (Texinfo) — v1.24

Mirror standard v1.24 changes:
- Add §8 Documentation (Texinfo) section (§8.1–§8.6)
- Renumber old §8–§15 → §9–§16 throughout (headers, body cross-refs, checklist)
- Add §8 checklist bullet in §16
- Update Skill Cross-References with Texinfo row
- Update frontmatter description and masthead to v1.24 / 2026-06-19
- Update intro text: "14-point checklist in §15" → "15-point checklist in §16"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: UnbreakableMJ