feat: add Pi and Oh My Pi badge colors

[timseriakov]

Summary

• add Pi and Oh My Pi to the frontend agent badge color map
• use the shared violet identity color matching Codbash: #a78bfa foreground with a translucent violet background
• keep the existing unknown-agent gray fallback unchanged

Related

• Supports agent keys introduced in feat(pi): add Pi and Oh My Pi support codbash#221

Verification

cd ./frontend
npm run build

cd ..
rm -rf server/public
cp -R frontend/dist server/public

cd ./server
npm start