Add tooltips for the side buttons and main buttons

[novoselt]

"Main buttons" are Save/Time travel/AI assistant. When they are small (which happens always with split frames), it is hard to guess what they are doing. "Save" does look familiar, but works very different in CoCalc because of quite aggressive Autosave, so could use some clarification too. Perhaps even mentioning the current autosave interval and how to configure it.

[novoselt]

Specifically for the "Save" button - when the frame is split, it becomes a small square with a floppy disk and, actually, cannot be used because there is nothing to save a lot of times. BUT - if there is an error saving, the icon changes to an abstract arrow, there is no tip what it does, and there is also no "Not saved" message on it, so it is not clear if the banner regarding saving issues is still valid or not. I would change the whole button to red, but keep the floppy disk icon, then it is clear that something is wrong with saving.

[novoselt]

Specifically for the Save button - "Not saved" message is rare, but when it does appear, there is no indication of why and what to do or not to do.