Choose viewed email account (or composite folder) from a dropdown rather than a list of all accounts and their folders

Is your feature request related to a problem? Please describe.

Right now all the email accounts are listed one after the other in the left column, making it hard to navigate through them (as a lot of scroll is needed) and to drop emails in the right folder (as sometimes it needs to be reached at the bottom of the accounts list).
At the same time, if I want to see the inbox (or the sent folder, the drafts...) of a particular account I need to look for its folder in the accounts+folders structure.

Describe the solution you'd like

I'd like it to be possible to choose the account (with the composite view as the default option) from a dropdown list.
Under the dropdown, replacing what now is the accounts+folders structure, could appear the specific folder-tree of the account. When the composite view is selected, "priority", "all inboxes" and "outbox" could be showed, or they could be always visible so that clicking on them after having selected a particular account from the dropdown makes the view automatically switch to composite.

This could free up space when the composite view is selected to add something useful as starred folders throughout the various accounts.

Describe alternatives you've considered

No response

Additional context

No response

No files, tests, or entry points are named. Start by reviewing the current left-column account and folder navigation, then map the requested dropdown and composite-view behavior. Done means the selected account's folders are shown, composite folders remain usable, and the navigation no longer requires scrolling through every account.