The Agent Skills standard (agentskills.io/specification) uses
`disable-model-invocation: true` to hide skills from auto-discovery.
OMP only recognized `hide: true`. This patch treats both as equivalent,
improving compatibility with skills authored for Pi, Claude Code, and
other harnesses following the standard.
Changes:
- Check `disableModelInvocation` (camelCase after frontmatter parsing)
in all 3 skill-loading paths
- Add `disableModelInvocation` to SkillFrontmatter type with JSDoc
- Add regression test for disable-model-invocation frontmatter
- Add changelog entry
Ref: https://agentskills.io/specification#frontmatter-required