implement an "account" pulldown menu in the frontend app, similar to the account pulldown menu in the nextjs

[DrXyzzy]

1. Sign into CoCalc.com and hover the cursor over "Account" at upper right.

2. Observe the Account pulldown menu:

   

3. Click "Your Projects" at top or "Projects" under the "Signed in as" notice and hover the cursor over "Account" at upper right as before:

   

4. Observe that the Account pulldown does not appear. Clicking on "Account" also does not display the pulldown.

[williamstein]

I changed the title from "app pulldown menu disappears when "projects" is selected", since it's not that the menu disappears.

It's a completely different application and almost everything about the entire navbar across the top is different. It would certainly be nice to also have a pulldown menu in the frontend app, and what goes there might be similar to what's in the nextjs app (maybe even exactly the same). However, the semantics of what it would do might be different, and the implementation would be completely different. For example, Account -> Projects in the opens a new tab right now in the nextjs app (maybe that is wrong, actually), but certainly shouldn't in the frontend app.

[williamstein]

I just want to note that this is actually pretty difficult because right now the account label is the Account prefs tab. If it were replaced by a dropdown menu, then there is no where to put the account prefs tab. So it's actually a pretty nontrivial design question, and this issue is now definitely unclear what it's really asking for. I.e., you want to replace an existing tab by a menu, but then where does all the content for that tab go? We have to figure that out.