Remove the Tier-B exclusivity qualifier from the quick-merge stage-2 fixture

[justinmclean]

Summary

A pr-management-quick-merge fixture adds a "Tier B glob only" qualifier that
does not exist in candidate-rules.md.

Background

The fixture's Tier-B definition is narrower than the rule it reflects. No case
hits the difference today because the current glob sets are disjoint, so the
suite passes. A future config change with overlapping globs would make fixture
and rule disagree, and the fixture would win, because it is what the eval grades
against. Fixtures should restate the rule, not tighten it.

Where to look

• evals/pr-management-quick-merge/stage-2-triviality/fixtures/system-prompt.md -
  the Tier-B definition carrying the qualifier.
• skills/pr-management-quick-merge/candidate-rules.md - the definition to match.

Acceptance criteria

• The fixture's Tier-B wording matches candidate-rules.md.
• No case's expected output changes, since the sets are disjoint today. If
  one does, that is a real finding worth calling out in the PR.
• The pr-management-quick-merge eval suite passes.

Estimated effort

~1 hour for someone new to the codebase.