fix: keep transient UI out of rollback state

[han4wluc]

Summary

• stop recording transient UI actions into rollback checkpoints
• split rollback batches into line and interaction sources so authored line state and player interactions are replayed separately
• keep save/load sanitization for legacy slots and add regression coverage for live rollback and load-then-rollback overlay behavior

Testing

• bun run test
• rtgl vt screenshot --wait-event vt:ready --item rollback/layered-view-restore.yaml
• rtgl vt report --diff-threshold 0.8 --item rollback/layered-view-restore.yaml
• rtgl vt screenshot --wait-event vt:ready --item save/load-rollback-transient-overlay.yaml
• rtgl vt report --diff-threshold 0.8 --item save/load-rollback-transient-overlay.yaml