Reorganize skill generation code for better domain separation:
- Move files from core/output/skill/ to core/skill/ (5 files)
- Move writeSkillOutput.ts from core/packager/ to core/skill/
- Create packSkill.ts to encapsulate skill generation logic
- Simplify packager.ts by delegating skill generation to packSkill()
- Add re-exports in outputGenerate.ts for backward compatibility
This change improves code organization by:
- Separating skill domain from output domain
- Reducing packager.ts complexity
- Centralizing all skill-related code in one location
