Design app hierarchy/account management

[daneden]

Currently there's incompleteness/inconsistency in how the app hierarchy is structured. This has the most potent impact on how accounts are managed and switched.

1. On iOS, the views are divided into three tabs: Projects, Deployments, and Account. Account switching changes context for the entire app.
2. On iPadOS and macOS, the views are shown in a sidebar navigation view with an account switcher at the top of the sidebar menu. Account switching (ideally) changes context for the windowed instance only.

The interaction pattern here either needs to be aligned across platforms or at least made reliable per platform idiom.

[daneden]

Minor update: good progress on iPadOS and macOS:

• [x] The sidebar now lists all authenticated accounts
• [x] Each account section has a context menu to delete an account
• [ ] I should still add a button to add a new account, as well as a “Manage accounts” view where users can reorder, delete, and add accounts