Add a flaky-test repair replay demo

[human-again]

Goal

Create a deterministic replay demo that shows Orbit detecting and repairing a flaky-test style failure.

Suggested scope

• Follow the existing examples/auth-rescue/ and examples/issue-search/ patterns.
• Use deterministic local code and tests only.
• Avoid external services, secrets, or network requirements.

Acceptance criteria

• MOCK=1 ./replay.sh <demo-name> completes successfully.
• The demo writes inspectable artifacts for validation, evaluation, and review.
• Tests cover the demo replay path.