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

[dieterbaier]

Summary

• Fixes Slice #22.1: Move included ADR/QS/R artifacts to section-level headings #23 as the first implementation slice for Fix included artifact heading levels and refresh dogfood example #22.
• Moves ADR, quality scenario, and risk artifacts from level-0 titles to section-level titles.
• Keeps internal artifact sections nested below the artifact title and offsets generated traceability includes accordingly.
• Updates root templates, root source artifacts, example templates, and example ADR/QS/R source artifacts consistently.

Verification

• ruby -Itest test/validate_metamodel_test.rb
• ruby scripts/validate-metamodel.rb
• ruby scripts/validate-metamodel.rb --docs example/src/docs
• asciidoctor -D /tmp -o akt-root-arc42.html src/docs/doc-001-arc42.adoc
• asciidoctor -D /tmp -o akt-example-arc42.html example/src/docs/doc-001-private-budget-arc42.adoc
• HTML spot check: root ADR/QS/R headings render below their owning chapters, with no ADR/QS/R h1 or h2 headings.

Notes

Root validation still reports existing bidirectional relation warnings. They are unchanged by this slice.