[Agent Builder] Remove round dependencies from event renderers and response actions

Remove the remaining requirement to construct or pass a conversation round when rendering events or using response actions.

- Replace toSyntheticRound and rawRound with the actual data each response action needs.
- Review UserMessageEvent/RoundInput and AgentTurn for remaining round dependencies, retaining reusable presentational components.
- Extract a shared frame only where it meaningfully removes duplicated presentation.
- Coordinate the dataset action’s replacement format or temporary disablement with its owners.
- Record feedback identity/API changes for when feedback is re-enabled; keep that work deferred.
- Do not restore Regenerate.