fix cli scroll flicker

[buffpesos]

Summary

• stop rebuilding the full CLI transcript on every agent state change by syncing chat history incrementally
• keep the main view mounted during normal operation and only re-render the overlay layer when selection or approval UI is active
• remove the timer-driven tool and working-indicator spinners so scrolling is not fighting 80ms redraws

Root cause

The CLI was clearing and rebuilding large parts of the pi-tui tree during live updates, and two animated indicators were still forcing continuous renders. That combination caused severe flicker while scrolling because the terminal kept repainting active lines instead of only reacting to real state changes.

Validation

• bun run typecheck
• bun test

✅ tested on macos