- Introduce Project sidebar item as the root of the tree hierarchy
- Support ProjectSession items for sessions spawned at project root
- Add project_overview_active flag and project_session_ids collection
- Implement auto-init dialog triggering via AutoInitKind enum
- Update context actions to include Project and ProjectSession variants
- Rebuild sidebar to always include Project item first, followed by its sessions
- Handle project expansion/collapse and activation in toggle_expand/activate_selected