fix: make skill frontmatter valid YAML

A ": " inside a plain-scalar description is a parse error; use a
folded block scalar instead.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

yarn-lock-separate-commit/SKILL.md

@@ -1,6 +1,7 @@
 ---
 name: yarn-lock-separate-commit
-description: yarn.lock in its own commit — use when changing Yarn dependencies (package.json deps, workspace renames, yarn install), when organizing or reviewing commits that touch yarn.lock, when a rebase conflicts on yarn.lock, or during a retcon. Every lockfile change ships alone as `chore: Update yarn.lock`, after the package.json commit that caused it.
+description: >-
+  yarn.lock in its own commit — use when changing Yarn dependencies (package.json deps, workspace renames, yarn install), when organizing or reviewing commits that touch yarn.lock, when a rebase conflicts on yarn.lock, or during a retcon. Every lockfile change ships alone as `chore: Update yarn.lock`, after the package.json commit that caused it.
 ---
 
 # yarn.lock in a separate commit