The existing frontmatter test only checks that a description is present, so all
three array-valued argument-hint declarations passed CI on main. Harnesses that
type-check the field reject the whole file, which is how the commands went
missing without anyone noticing.
Add an assertion scoped to argument-hint only. A blanket 'no flow sequences in
frontmatter' rule would be wrong: allowed-tools is a legitimate list in
marketing-campaign.md and skill-create.md.
Verified both directions -- on main the new test fails and names exactly
code-review.md, cost-report.md, and orch-review.md; on this branch the suite
passes 96/96.
zakyirsyaad