verification:measure description has no 'Use when:' trigger phrasing

[kyle-sexton]

Problem

scripts/check-changed-skills.sh reports on plugins/verification/skills/measure:

WARN: description has no 'Use when:' trigger phrasing — a description is a trigger spec, not a summary

A skill description is what Claude matches against to decide whether to load the skill. Without trigger phrasing it reads as a summary of what the skill is rather than a specification of when to reach for it, so the skill is less likely to fire when it should.

Scope

Pre-existing — surfaced during PR #2161, which touched measure/context/metrics.md but not the SKILL.md frontmatter, and confirmed by git diff origin/main at the time. Carried as a noted follow-up on #2161 and again on #2169; filing it so it stops being a footnote on unrelated PRs.

Fix

Rewrite the description to carry Use when: triggers in the marketplace's house style — the concrete phrases a user would actually type, not a paraphrase of the skill's purpose. Compare the sibling skills in the same plugin (confirm, setup) and codebase-health:audit for the established shape.

Worth checking at the same time whether any other skill carries the same warning; the gate reports it per changed skill, so a repo-wide pass would need --all or an equivalent sweep rather than the base-ref diff form.