skill: document trust gate, sandboxed vetting, and learn command
Update using-vit SKILL.md:
- Section 4: add vit learn with trust gate behavior documented
- Section 4: add trust gate docs to vit remix
- Section 5: document sandboxed sub-agent vetting (--trust --confirm)
- Section 5: add vit vet --dangerous-accept as human-only
- Section 7: add .vit/dangerous-accept to data files
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>