fix(gates): read leading-whitespace frontmatter in check-skill-version-bump

read_version required --- at byte 0 while skill-size-check accepts
leading blank lines, so a file one gate passed the other reported as
unversioned, and an unversioned merge-base side let an unbumped change
through. Match FRONTMATTER_RE, add case 39, and describe the main-tip
check and fail-closed cases in the hook entry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -189,16 +189,19 @@ repos:
 
       - id: check-skill-version-bump
         name: Check changed skills bump metadata.version
-        description: On every push, fail if a skill directory changed (tests/ excluded) since the merge-base with main without its SKILL.md metadata.version rising (ADR-0022)
+        description: On every push, fail if a skill directory changed (tests/ excluded) since the merge-base with main without its SKILL.md metadata.version rising above both that merge-base's and main's tip's (ADR-0022)
         entry: bash scripts/check-skill-version-bump.sh
         language: system
         stages: [pre-push]
         pass_filenames: false
         always_run: true
-        # Baseline is the merge-base with origin/main (falling back to main),
-        # not the remote branch tip: readers install from main. Fails closed
-        # when no main ref resolves. Merges through Gitea's merge button run no
-        # local hook, so they bypass this.
+        # "Changed" is measured from the merge-base with origin/main (falling
+        # back to main), not the remote branch tip: readers install from main.
+        # The version must also beat main's tip, so two branches making the same
+        # bump cannot both land. Fails closed when no main ref resolves, when
+        # there is no merge-base, or when only local main resolves and already
+        # contains the pushed commit. Merges through Gitea's merge button run no
+        # local hook, so they bypass this. See docs/spec/gates.md.
 
       - id: validate-marketplace
         name: Validate marketplace manifest