[MetaROR] Final formatting, consistency & referencing (pre-release)

Formatting, consistency and referencing tasks to complete before releasing the next version. Some can be agent-assisted but each needs a human review pass.

- [ ] **Use "this handbook" consistently** — the text currently alternates between "paper", "article" and "handbook". This needs context judgement (not every "paper" refers to the handbook), so review each change rather than running a blind find-and-replace. (R2)
- [ ] **Add introductory lines at the beginning of each section** to orient casual readers. (R2)
- [ ] **Final referencing pass** — fix broken citations and verify DOIs, citation metadata and reference completeness across the handbook before release.

**Related existing issues** (whoever takes this owns these too):
- #3 Broken citations

**Handled in other issues:**
- Add date-accessed timestamps to all web references → *Automatable tasks*
- Conceptual terminology/typology alignment → *Cross-cutting editorial changes*

Review the handbook sections and the related broken-citations issue #3 first; no specific files or tests are named. Check terminology in context, add orienting lines to each section, and verify citations, DOIs, metadata, and reference completeness across the handbook. Done means all listed pre-release checks are reviewed by a human.

Written by the indexing model from the issue text.