fix(config-yaml): unroll markdown prompt files as prompts

[McGluut]

Summary

• pass the target section into block resolution so markdown files referenced from prompts unroll as prompt blocks instead of rules
• keep existing markdown fallback behavior for rules and other sections
• add a regression test for prompts: - uses: file://...md

Fixes #12412.

Tests

• npm test -- --runTestsByPath src/load/unroll.test.ts from packages/config-yaml
• npm run build from packages/config-yaml
• npx prettier --check packages/config-yaml/src/load/unroll.ts packages/config-yaml/src/load/unroll.test.ts
• git diff --check

---

Summary by cubic

Fixes incorrect unrolling of markdown files in the prompts section so they become prompt blocks instead of rules. Keeps existing markdown fallback for rules and other sections, and adds a regression test in packages/config-yaml.

• Bug Fixes
  • Pass the section hint through block resolution so prompts markdown parses as prompts.
  • Preserve markdown-to-rule fallback for rules and other sections.
  • Add test for prompts: - uses: file://...md.

^{Written for commit 2aed834. Summary will update on new commits. Review in cubic}

[github-actions]

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[cubic-dev-ai]

No issues found across 2 files

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[McGluut]

I have read the CLA Document and I hereby sign the CLA