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.Core/DTOs/ChatDtos.cs

@@ -12,7 +12,7 @@ public record MessageDto(
     string? AttachmentUrl,
     string? AttachmentFileName,
     DateTimeOffset SentAt,
-    EmbedDto? Embed = null);
+    List<EmbedDto>? Embeds = null);
 
 public record ChannelDto(
     Guid Id,