feat: enhance IRC support with display name handling, private channel tracking, and connection identification

src/EchoHub.Core/Constants/HubConstants.cs

@@ -4,6 +4,12 @@ public static class HubConstants
 {
     public const string ChatHubPath = "/hubs/chat";
     public const string DefaultChannel = "general";
+
+    /// <summary>
+    /// Connection-id prefix for IRC gateway connections. The presence tracker uses it to
+    /// tell IRC-only users apart from native (SignalR) clients.
+    /// </summary>
+    public const string IrcConnectionIdPrefix = "irc-";
     public const int DefaultHistoryCount = 100;
     public const int MaxMessageLength = 2000;
     public const int MaxImageSizeBytes = 10 * 1024 * 1024; // 10 MB

src/EchoHub.Core/DTOs/ChatDtos.cs

@@ -10,7 +10,8 @@ public record MessageDto(
     string ChannelName,
     DateTimeOffset SentAt,
     List<AttachmentDto>? Attachments = null,
-    List<EmbedDto>? Embeds = null);
+    List<EmbedDto>? Embeds = null,
+    string? SenderDisplayName = null);
 
 /// <summary>
 /// A file attached to a message. <see cref="AsciiPreview"/> holds the color-tag art for

src/EchoHub.Core/DTOs/ProfileDtos.cs

@@ -30,6 +30,7 @@ public record UserPresenceDto(
     string? NicknameColor,
     UserStatus Status,
     string? StatusMessage,
-    ServerRole Role);
+    ServerRole Role,
+    bool IsIrc = false);
 
 public record AvatarUploadResponse(string AvatarAscii);