feat(repo): teach /verify-spec to read acceptance criteria from a GitHub issue

[orioltf]

Parent: #297 · Found by the comprehensive review of #298 (L13)

Problem

.claude/skills/verify-spec/SKILL.md locates specs as docs/issues/<slug>/PRD.md. Since upstream
v1.1, /to-spec publishes the spec as a GitHub issue and writes no file — so on any Feature specced
that way the skill finds nothing.

#298 added the scope limit so the skill now says "this Feature's spec is a GitHub issue, which this
skill cannot read yet" instead of reporting no match, which read as a missing spec. That is honest, not
useful. This issue closes the gap.

Acceptance criteria

• Given an issue number or a slug that matches an issue title, /verify-spec reads the acceptance
  criteria from the issue body via gh issue view
• It also reads the criteria of the issue's sub-issues, since /to-tickets puts them on children
  rather than the parent
• File-based specs keep working unchanged — the existing docs/issues/<slug>/PRD.md path is not
  regressed, and both are tried before reporting no match
• Each criterion is still reported ✓ PASS / ✗ FAIL with a one-line evidence note
• The scope-limit paragraph added in chore: de-dogfood unic-archon-dlc and upgrade Matt's skills to upstream main #298 is replaced by the real behaviour

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🤖 Filed with Claude Code.