Fix TUI lockups under log floods

[carlosrivera]

Summary

• Split output events into a dedicated channel so input/shutdown stays responsive under heavy logs.
• Throttle TUI redraws to ~30fps and drop excess output with a summary line in TUI mode.
• Document a manual smoke test for high-volume output.

Testing

• manual: cargo run -- -- --name spam -- sh -c "yes"

Fixes #9.