Installation Model: Canonical Directory + Symlinks
Skills are stored in a canonical directory (.agents/skills/), and each platform directory links to it via relative symlinks.
.agents/skills/my-skill/ ← actual files (canonical)
.codebuddy/skills/my-skill/ → symlink → ../../.agents/skills/my-skill/
.gemini/skills/my-skill/ → symlink → ../../.agents/skills/my-skill/