* fix(tui): steady transcript scrollbar
Keep the visible scrollbar tied to committed viewport position while virtual history can still prefetch against pending scroll targets, and preserve drag grab offset synchronously for native-feeling scrollbar drags.
* fix(tui): smooth precision wheel scroll
Replace the opt-scroll throttle with frame-sized coalescing so modifier wheel gestures stay line-precise without stepping.
Keep the latest prompt sticky while the viewport is in live assistant output beyond history, and clear stale sticky state at the real bottom using fresh scroll height.
