Ship a GitHub workspace inside the native launcher using the Stacks GitHub core package.
Acceptance:
- Search repositories, issues and pull requests without requiring an account for public results.
- Offer assigned issues, requested reviews and notifications when connected.
- Persist the optional repository scope locally.
- Store the optional token in macOS Keychain and remove it on disconnect.
- Debounce requests, cancel stale results, bound network time and surface API errors.
- Send only GitHub-category queries to GitHub.
- Open verified GitHub HTTPS result URLs in the default browser.
Follow-up: evaluate first-party OAuth onboarding before replacing manual token entry; do not ship an embedded client secret.