fix(governance): scope qualitative checks by artifact

[Malakof]

Summary

• generate body-completeness guidance from the artifact kind
• make native sub-issue review apply only to [EPIC] issues
• explicitly allow acceptance-criteria checklists
• add deterministic PR, ordinary-issue, and epic prompt tests

Context

The v1.4.1 format checker applied epic-only sub-issue guidance to every artifact. On Malakof/crystal-capabilities#7, run 29309706774 requested a Markdown checklist; after adopting it, run 29309759829 warned that the checklist should be native sub-issues. The prompt also let issue-template heading requirements leak into PR review.

Tracked by Malakof/crystal-platform#411.

Acceptance criteria

• PRs cannot receive native-sub-issue or child-checklist advice.
• Ordinary issues cannot receive epic child-tracking advice.
• EPIC issues still prefer native sub-issues over mirrored - [ ] #N entries.
• Acceptance-criteria checklists remain allowed.
• Deterministic tests cover all three artifact classes.

Out of scope

• suppressing annotations
• making the qualitative check blocking
• weakening title, label, or epic governance

Validation

• python3 -m unittest discover -s tests -v — 11 passed
• python3 -m py_compile scripts/*.py
• git diff --check