Flexible toolbar layout

[fllmn]

Discussed in #135, the toolbar currently sets the minimum width of the application. I'm not convinced this is the best way to solve but I wanted to give Gemini CLI a go (it didn't do that well), anyhow

This collapses the machine controls when the UI is narrowed down.

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The two issues I see are, machine controls are the most useful buttons (IMO) and making them less accessible is disservice to the user, secondly the "trigger" is based on a fixed width, ~1400px which is always a poor choice as it would have to be updated any time buttons change.

What could be interesting to discuss in case

1. What buttons should be grouped and hid when width is narrowed down
2. How can the toolbar manage its width to decide if it needs to collapse to fit the window.