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>

scripts/check-skill-version-bump.sh

@@ -175,12 +175,14 @@ done < "$CHANGED_FILE"
 # python3 crashing, PyYAML failing to import — is a non-zero exit with no OK /
 # INVALID line, which the caller reports as a read failure, never as a missing
 # version. Bytes are decoded explicitly so the caller's locale cannot turn a
-# non-ASCII SKILL.md into a crash; `\s*` before each `\n` absorbs CRLF.
+# non-ASCII SKILL.md into a crash; `[ \t\r]*` before each `\n` absorbs CRLF.
+# Whitespace before the opening `---` is accepted, matching FRONTMATTER_RE in
+# factory-audit's lib-boundary-resolver.sh, which skill-size-check applies.
 read_version() {
   python3 -c '
 import re, sys, yaml
 text = sys.stdin.buffer.read().decode("utf-8-sig", errors="replace")
-m = re.match(r"---[ \t\r]*\n(.*?)\n---[ \t\r]*(\n|\Z)", text, re.S)
+m = re.match(r"[ \t\r\n]*---[ \t\r]*\n(.*?)\n---[ \t\r]*(\n|\Z)", text, re.S)
 data = None
 if m:
     try: