Extends scripts/ci/validate-skills.js to also scan docs/{locale}/skills/
translated mirrors, not just curated skills/. Adds detection for the
YAML defect classes from #2630 without a parser dependency: unquoted
values containing ": " (glued next key / dropped quoting), values
starting with the reserved '@'/'`' indicators, and missing frontmatter
blocks entirely (required only for docs mirrors; curated skills/ keeps
its existing tolerant behavior).
