Add user PIN protection (#719)

## Description
Adds (back) the ability to set a per-user PIN. This is required to
switch to the user. If the user has a PIN, this overrides and ignores
the "Sign in automatically" setting for that user.

The PIN consists of any combination of D-Pad directional buttons. If you
forget the PIN, you can click the button to login via the server instead
(ie QuickConnect or username/password) which will also remove the PIN so
you can set a new one if desired.

### Related issues
Closes #268 
Replaces #398
Related to #321 & #356

### Screenshots
![enter_pin
Large](https://github.com/user-attachments/assets/aa25364d-1266-410d-846e-8dc32c56a794)

app/src/main/java/com/github/damontecres/wholphin/ui/setup/SwitchUserContent.kt

@@ -118,13 +118,11 @@ fun SwitchUserContent(
                     users = users,
                     currentUser = currentUser,
                     onSwitchUser = { user ->
-                        // TODO PIN-related
-//                        if (user.pin.isNotNullOrBlank()) {
-//                            switchUserWithPin = user
-//                        } else {
-//                            viewModel.switchUser(user)
-//                        }
-                        viewModel.switchUser(user)
+                        if (user.hasPin) {
+                            switchUserWithPin = user
+                        } else {
+                            viewModel.switchUser(user)
+                        }
                     },
                     onAddUser = { showAddUser = true },
                     onRemoveUser = { user ->