open source is social v-it.org

complete vit branding across CLI and repo master

Extend brand mark/prefix to remaining commands (adopt, follow, remix, vet, vouch). Add SVG assets to docs/brand/ and docs/badge/ for hosting on v-it.org. Add vit-enabled and social-open-source badges to README. Generate .vit/README.md from brand template on init. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>