Show warning for future unsupported server version (#2115)

## Description
Now that Jellyfin 12 has been out for over six weeks, it's time to start
considering dropping support for Jellyfin 10 & 11 as part of #1640.

This PR adds a warning message on the switch server, switch user, &
preferences pages if the current server version is <12.

### Related issues
See https://github.com/damontecres/Wholphin/discussions/1640 for further
discussion!

### Testing
Emulator w/ faked data

## Screenshots
N/A, reuses the same error message space

## AI or LLM usage
None

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

@@ -122,5 +122,7 @@ class WholphinApplication :
             private set
 
         val minimumServerVersion: ServerVersion = Jellyfin.minimumVersion
+
+        val newMinimumServerVersion: ServerVersion = ServerVersion(12, 0, 0)
     }
 }