Implement scenario history, version comparison, and trace viewer/export review surfaces

[kalen-releasedgroup]

Summary

Complete the review experience for version evolution and replay/export evidence.

Scope

• Add scenario history and version comparison views.
• Add trace viewer integration or trace review affordances.
• Improve export/review surfaces for generated artefacts and replay evidence.

Requirement Links

• Sections 5.3.4, 7.5, 9.4, 9.5, 18.3

Dependencies

• Scenario versioning
• Replay diagnostics
• Generated artefact workflow

Exit Criteria

• Users can inspect scenario history and compare versions.
• Trace review is accessible from replay diagnostics.
• Review surfaces support hardening-phase workflows.