Tooltip on price in TaskHeader showing subsessions becomes unusable with tens of subagents

The tooltip on the price in the TaskHeader that shows subsessions becomes unusable when there are tens of subagents.

Consider:
- Showing the last session on top
- Aggregating some older info as the number of subagents grows

<img width="150" height="943" alt="Image" src="https://github.com/user-attachments/assets/7795244a-bc3a-49c1-bae0-a84179a6aaa5" />