Show public users when switching users (#1358)

## Description
Show the public users (ie "Hide this user from login screens" is
unchecked) if the server has any. Previously, all users had to be
explicitly added by username or quick connect.

This PR also refactors the server & user pages to use modern state flows
and deletes some unused code.

### Related issues
Closes #600

### Testing
Emulator

## Screenshots
N/A

## AI or LLM usage
None

app/src/main/java/com/github/damontecres/wholphin/MainContent.kt

@@ -85,7 +85,7 @@ fun MainContent(
 
                         is SetupDestination.UserList -> {
                             SwitchUserContent(
-                                currentServer = key.server,
+                                server = key.server,
                                 Modifier.fillMaxSize(),
                             )
                         }