Implement targeted rerun support for full replay, current-step onward, and single-step diagnostics

[kalen-releasedgroup]

Summary

Improve replay troubleshooting speed with targeted rerun controls.

Scope

• Support full replay reruns.
• Support current-step-onward reruns where valid.
• Support single-step diagnostic reruns where valid and safe.

Requirement Links

• FR-REP-004
• Section 9.5

Dependencies

• Replay workspace and diagnostics state

Exit Criteria

• Supported rerun modes are available through the UI.
• Unsupported reruns are blocked with clear rationale.
• Rerun history remains traceable.