test(review): pin that codex $name skills survive the legacy repair + native invocation

The user asked whether configured codex $code-reviewer skills are retained after #1749's legacy-config repair merged in. They are, by two independent guards; these tests lock that so a future migration edit can't clobber real skills:

• normalizeLegacyCodexDefaultSkills only rewrites codex's exact ["/review"] artifact; a $code-reviewer config and multi-skill configs pass through untouched.
• codexNativeSkillInvocations rewrites only slash-form to $; $name and plain text pass through verbatim.