Allow app to have no tabs open

[jameskerr]

Let's be more like vscode than google chrome. Since our sidebar offers alot of navigation, let's allow a state where there are no tabs open. The user can still click pools and queries in the sidebar.

[mason-fish]

@jameskerr did you have an empty state in mind to fill the main page in this tabless scenario?

[jameskerr]

I just took a swing at this and missed. Here are my thoughts for the next attempt.

Much of the app depends on a tab being active. We'd need the whole sidebar and app wrapper components to have no dependencies on state from the "active tab".

[philrz]

Verified in Zui commit 05f017b.

The linked PR #2797 changed more than just allowing for the app to have no tabs open. Now each window will only be able to connect to one lake at a time, so as shown in the attached video, changing the lake connection in the drop-down menu changes the tabs shown to the ones previously established when connected to that lake. The video also shows how the app does indeed now allow all tabs to be closed. When in that "no tabs" state, currently just the big Zed logo background image is shown in the large/blank area, so #2804 has been opened to remind us to put something more helpful there eventually.

Verify.mp4

Thanks @jameskerr!