Phase-23 concrete accepted-evidence set membership assignment record

[kenanay]

This PR changes only PHASE23_CONCRETE_ACCEPTED_EVIDENCE_SET_MEMBERSHIP_ASSIGNMENT_RECORD.md and accepts only a bounded concrete accepted-evidence set membership assignment record boundary.

It does not assign accepted-evidence set membership, create accepted evidence, accept any evidence item, accept validator output, accept receipt evidence, or authorize runtime/source/package/source-merge/capability/registry/trust/deployment/distribution/kernel ABI/syscall/workflow-threshold/baseline/dependency/Ring0 authority.

Validation:

• git diff --check
• git diff --cached --check before commit

Scope exclusions:

• docs/roadmap/CURRENT_PHASE unchanged
• PHASE21_FIRST_BOUNDED_IMPLEMENTATION_ACTUAL_SKELETON_PR_DESIGN.md remains PR-disjoint

[github-actions]

Ayken Advisory

• Authority: none
• Confidence: -
• Risk: high
• Nearest Verified Ancestor: -
• Distance: - commits
• Gates: PASS

Advisory only — does not override CI authority.