Reduce UI footprint for compression events

[sehoon38]

What would you like to be added?

Reduce the impact of more compression events, by reducing the UI footprint when this happens.

Why is this needed?

As compression happens more frequently (at 20% threshold), it should be less disruptive to the user experience.

Additional context

• Part of Epic: [Epic] Compression in Gemini CLI #23905
• DRI: Keith Guerin
• Reference: style(ui): iterate on loading and error strings for precise conciseness #22087

[rnett]

IMO the biggest impact is the slowness and how it blocks the UI during that time. I don't see why it couldn't be done in the background.