Slice #22.1: Move included ADR/QS/R artifacts to section-level headings

[dieterbaier]

Parent: #22

Goal

Adopt the canonical heading policy from the parent issue discussion: architecture detail artifacts that are intended to be included into an assembled/wrapping document start at section level 1 (==), not document level 0 (=).

This applies at least to ADR, quality scenario, and risk artifacts.

Background

The parent issue initially considered preserving standalone = headings and compensating with leveloffset. The follow-up decision is different:

an ADR should start with Level 1 (== ...). If one would really like to have such a document rendered standalone on Level 0, you can still wrap that document with a dedicated Level 0 document

So the source artifacts themselves should match their normal include context.

Scope

• Update templates/adr.adoc, templates/quality-scenario.adoc, and templates/risk.adoc so their first visible heading is ==.
• Update existing root source artifacts:
  • src/docs/arc42/09-architecture-decisions/adr-*.adoc
  • src/docs/arc42/10-quality-requirements/qs-*.adoc
  • src/docs/arc42/11-risks-and-technical-debt/r-*.adoc
• Update example templates and example ADR/QS/R source artifacts consistently, or explicitly defer example changes to the dogfood slice if that keeps review smaller.
• Preserve YAML front matter, stable IDs, anchors, statuses, summaries, and traceability includes.
• Check whether generated traceability fragments still land at the intended child level after the heading change.

Acceptance Criteria

• ADR/QS/R templates start with ==, not =.
• Existing ADR/QS/R source artifacts in the root docs start with ==, not =.
• No level-0 heading remains in an included ADR/QS/R artifact.
• Rendered root arc42 output no longer promotes ADR/QS/R artifacts to top-level sibling chapters.
• Validation and render checks pass.