[Demo][Rubber Duck] Critique checkout reliability plan

## Demo goal
Demonstrate Rubber Duck Agent second-opinion workflow.

## Prompt to run
"Design a migration plan for checkout quote reliability in `demo-app/server.js` with rollback, SLOs, and observability. Then critique your own plan for hidden risks."

## Expected output
- Initial plan
- Critique of risks/tradeoffs
- Revised safer plan

## Presenter cue
Use this issue text directly as the terminal prompt for Rubber Duck in Copilot CLI.

Use the issue text directly as the terminal prompt for Rubber Duck in Copilot CLI, with demo-app/server.js as the referenced application entry point. Check that the result includes an initial checkout reliability plan, a critique of risks and tradeoffs, and a revised safer plan with rollback, SLOs, and observability.

Written by the indexing model from the issue text.