feat: Add notification sound functionality and embed support

- Introduced NotificationConfig to manage notification settings, including sound file.
- Added Notification.mp3 asset for notifications.
- Implemented NotificationSoundService to handle playing notification sounds.
- Enhanced ChatRenderer and MainWindow to support emoji rendering.
- Updated MessageDto to allow multiple embeds per message.
- Modified LinkEmbedService to fetch multiple embeds from message content.
- Added data migration for legacy embed JSON format to new array format.
- Adjusted embed handling in ChatService and IrcMessageFormatter to accommodate multiple embeds.
- Updated HubConstants for new embed dimensions and limits.

src/EchoHub.Client/Config/ClientConfig.cs

@@ -5,6 +5,13 @@ public class ClientConfig
     public List<SavedServer> SavedServers { get; set; } = [];
     public AccountPreset DefaultPreset { get; set; } = new();
     public string ActiveTheme { get; set; } = "Default";
+    public NotificationConfig Notifications { get; set; } = new();
+}
+
+public class NotificationConfig
+{
+    public bool Enabled { get; set; } = true;
+    public string? SoundFile { get; set; }
 }
 
 public class SavedServer