Demonstrate basectl workspace agent-brief and basectl workspace onboarding using the base+base-demo peer layout

[codeforester]

Summary

base-demo's Quick Start already sets up the exact peer-checkout layout (base and base-demo cloned side by side) that basectl workspace agent-brief and basectl workspace onboarding are designed for, but neither command is demonstrated.

Details

• base v1.7.0 added basectl workspace agent-brief (reports repo baseline, agent-guidance, AI-context, environment, and validation evidence for a workspace handoff) and basectl workspace onboarding (summarizes first-day repository readiness, missing clone actions, and setup/check/test commands from a workspace manifest), per base's CHANGELOG.md [1.7.0] section.
• base-demo's README already documents basectl workspace status --manifest workspace.yaml.example, so the workspace-level command family is partially demonstrated, but these two newer commands aren't mentioned anywhere in README, demo.sh, or docs.

Impact

These commands are a natural fit for base-demo's stated role of showing "a credible multi-language, infrastructure-backed project" in a multi-repo workspace context, and for new users evaluating whether Base can summarize workspace/onboarding state before committing to it.

Suggested fix

Add basectl workspace agent-brief and basectl workspace onboarding (against workspace.yaml.example) to the README Quick Start and/or demo/demo.sh, alongside the existing workspace status step.