Implements issue #1524. The agents actor remove command now displays:
- Actor Removed panel showing Name, Provider, and Model
- Impact panel showing Sessions, Active Plans, and Actions Referencing (with conservative estimates)
- Cleanup panel showing Config status and orphaned Contexts
- Success message: ✓ OK Actor removed
Note: Impact metrics currently show 0 affected items. Future enhancements can integrate
with session/plan subsystems to compute actual impact values.