Style side panel buttons and toggle terminal

[laurensvalk]

• Styles the doc button as blue
• Adds a terminal toggle button
• Adds a close all button

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reason 1: Generalize side panel

We'd like to use this for more than just docs, such as a camera view or telemetry.

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reason 2:

This fixes some usability issues for beginning users:

• When dragging the terminal or docs to nearly closed, it could be hard to know where they went. Clicking the docs button would not make it re-appear. The buttons will now restore them to default size.
• The docs button was harder to discover since it looked like an character in the editor. Now it looks like the other buttons.

new-2026-03-30_14.50.02.mp4

[dlech]

Does clicking the "Close all panels" button again restore all panels the way they were before closing? As a user, this is the behavior I would expect.

I would also expect "app: Preserve terminal state on hide." to be squashed with the previous commit. I was looking at each commit individually and almost made a comment about how the previous commit was broken. Then I saw the next commit that fixes it.

And I would like to see if we can find something better than the resetSplitterSize() hack.

[dlech]

This should use local storage so that it stays in the same state when the app is restarted.

[dlech]

I didn't see anything explaining why this value is changed.

[laurensvalk]

Does clicking the "Close all panels" button again restore all panels the way they were before closing? As a user, this is the behavior I would expect.

This doesn't quite work for the file browser, so I've dropped this particular addition. We can consider it for a future round.

I didn't see anything explaining why this value is changed.

Will save this for a future generic defaults overhaul too and drop it here.

I would also expect "app: Preserve terminal state on hide." to be squashed with the previous commit. I was looking at each commit individually and almost made a comment about how the previous commit was broken. Then I saw the next commit that fixes it.

Done.

And I would like to see if we can find something better than the resetSplitterSize() hack.

I spent some time at this and it doesn't seem trivial. Doing it the "right" way seems to break in numerous ways, like losing the scroll or destroying the editor. This dependency seems to be built to use only the initial state.