feat(contrib): file agent-suggestion issues as the logged-in user
Thread the user's GitHub token (from their device-flow login, which carries
repo scope) into the pipeline and use it to file agent-suggestion issues, so
contributions are attributed to the person who surfaced the content. A
configured IRIS_GITHUB_TOKEN still overrides this to file under a bot account
instead. Adds a transparency note to the demo sign-in.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>