Cleanups

Move keyboard/event reads in the TUI to a separate thread or async/io loop
Keep UI and orchestrator in sync (i.e. messages display out of order if you queue up many.)
update_scroll auto-follows in Insert mode, yanking viewport to bottom on mode switch. Only auto-follow when new content arrives (in drain_ui_events), not every frame.
G sets scroll to u16::MAX and relies on update_scroll clamping. Compute actual max_scroll inline, or document the contract that update_scroll must always run before render.
:clear clears TUI state immediately but sends ClearHistory to orchestrator async. A mid-stream response can ghost back in after clear. Need synchronization (e.g. clear on TurnComplete, or have orchestrator ack the clear).
Command overlay width: (out.width / 2).max(80) makes overlay full-bleed on 80-col terminals. Consider .max(40) or a different minimum.