Previously, the auto-scroll LaunchedEffect was keyed to `state.streamingMessage?.content?.length`, which resulted in the scroll animation coroutine being cancelled and restarted for every single token received during message generation. This caused a heavy performance hit and interrupted smooth scrolling.
This commit updates the `LaunchedEffect` key to use `state.streamingMessage != null` instead. The scroll-to-bottom logic now appropriately initiates when a message *begins* streaming (or finishes thinking), while avoiding continuous job restarts as the payload streams in.
Resolves#274
M57
858f4dce1d