fix: add CommonJS require export

[xianzuyang9-blip]

Summary

• add a CommonJS build output under dist/cjs
• expose that output through the package exports.require condition
• add a packaged CommonJS consumer regression test that installs the local package and verifies require("@mozilla-ai/otari")

Fixes #7.

Verification

• npm run lint
• npm run typecheck
• npm run test:unit
• npm run build
• npm pack --dry-run