Flatter, easier-to-scan sidebar
Sessions now display in a single-level list instead of a nested hierarchy, making the sidebar easier to scan and switch between.
Improvements
- Flatter sidebar layout: sessions are no longer nested — everything lives at the same level so the panel stays clean and easy to navigate.
- Refreshed derived-session icons that better reflect their relationship without cluttering the sidebar.
- Removed the inline prompt nudging you to spawn new sessions, for a less noisy sidebar.