Implement step-level replay status streaming and replay workspace UI

[kalen-releasedgroup]

Summary

Give authors real-time visibility into replay progress and outcomes.

Scope

• Stream replay status and step-level execution results to the UI.
• Implement the replay workspace with status, result feed, and diagnostic navigation.
• Preserve operation state across reconnects where reasonable.

Requirement Links

• FR-REP-001, FR-REP-004
• Sections 9.5, 10.2, 15.6

Dependencies

• Replay orchestration
• SignalR baseline

Exit Criteria

• Replay progress is visible live in the UI.
• Users can view step-level pass/fail state.
• The replay workspace is usable for long-running operations.