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/Constants/HubConstants.cs

@@ -15,9 +15,10 @@ public static class HubConstants
     public const int AsciiArtHeightHalfBlock = 80;
 
     // Link embed constants
-    public const int EmbedThumbnailWidth = 24;
-    public const int EmbedThumbnailHeight = 12;
-    public const int EmbedMaxDescriptionLength = 200;
+    public const int EmbedIconWidth = 12;
+    public const int EmbedIconHeight = 6;
+    public const int EmbedMaxDescriptionLength = 500;
     public const int EmbedMaxHtmlBytes = 64 * 1024; // 64 KB
     public const int EmbedFetchTimeoutSeconds = 3;
+    public const int EmbedMaxUrlsPerMessage = 3;
 }

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,