Replace app icon with LlamaCasty brand figure

- Assets/llamacasty-icon.png: new brand llama figure (no text)
- Assets/llamacasty-icon.ico: converted from PNG for executable
- Assets/llamacasty-logo.jpg: full logo with text
- ytLive.csproj: updated ApplicationIcon and Resource references
- All XAML windows: updated Icon references to new file

Models/Source.cs

@@ -11,7 +11,8 @@ public enum SourceType
     Image,
     TextOverlay,
     Countdown,
-    WebSource
+    WebSource,
+    ChatBox
 }
 
 public enum ClipShape
@@ -105,4 +106,39 @@ public class Source : SceneElement
     // Web source config
     private string? _webUri;
     public string? WebUri { get => _webUri; set => Set(ref _webUri, value); }
+
+    // Chat box config (TASK 3.18)
+    private double _chatFontSize = 16;
+    public double ChatFontSize
+    {
+        get => _chatFontSize;
+        set => Set(ref _chatFontSize, Math.Clamp(value, 8, 72));
+    }
+
+    private string _chatFontColor = "#FFFFFF";
+    public string ChatFontColor { get => _chatFontColor; set => Set(ref _chatFontColor, value); }
+
+    private string _chatBackgroundColor = "#80000000";
+    public string ChatBackgroundColor { get => _chatBackgroundColor; set => Set(ref _chatBackgroundColor, value); }
+
+    private int _chatMaxMessages = 5;
+    public int ChatMaxMessages
+    {
+        get => _chatMaxMessages;
+        set => Set(ref _chatMaxMessages, Math.Clamp(value, 1, 20));
+    }
+
+    private bool _chatShowTimestamps = true;
+    public bool ChatShowTimestamps { get => _chatShowTimestamps; set => Set(ref _chatShowTimestamps, value); }
+
+    private bool _chatShowBadges = true;
+    public bool ChatShowBadges { get => _chatShowBadges; set => Set(ref _chatShowBadges, value); }
+
+    private string _chatMemberColor = "#e94560";
+    public string ChatMemberColor { get => _chatMemberColor; set => Set(ref _chatMemberColor, value); }
+
+    private string _chatSuperChatColor = "#eab308";
+    public string ChatSuperChatColor { get => _chatSuperChatColor; set => Set(ref _chatSuperChatColor, value); }
+
+    public bool IsChatBox => Type == SourceType.ChatBox;
 }