- Add fetchDiscoveredSkills() to fetch all discovered skills with enabled state
- Add toggleExecutionSkill() to toggle skill enabled/disabled state
- Add fetchSkillsCatalog() to search the skills.sh catalog with query and limit
- Export skills types (DiscoveredSkill, CatalogEntry, CatalogFetchResult, ToggleSkillResult) for use by hooks/components
- Add comprehensive test coverage for all three API functions
