Fix rollback to restore settled presentation state

[han4wluc]

Summary

• settle rollback renders so restored lines skip reveal replay and transition replay
• add a regression test for rollbacked render state restoration
• add a 10-line rollback VT sandbox plus accepted reference for manual and VT coverage

Testing

• bun test spec/RouteEngine.rollbackRenderState.test.js
• bun run vt:report