Fix audio track label showing "Original" instead of "Unknown"

Changed the default audio track content type from "Unknown" to "Original"
when the content type is not specified. This provides a more accurate
description for the default audio track.

Model/Stream.swift

@@ -203,7 +203,7 @@ class Stream: Equatable, Hashable, Identifiable {
         }
 
         var description: String {
-            "\(displayLanguage) (\(content ?? "Unknown"))"
+            "\(displayLanguage) (\(content ?? "Original"))"
         }
 
         var isDubbed: Bool {