feat: enhance message broadcasting to exclude sender's connection and improve IRC compliance

src/EchoHub.Server.Irc/IrcBroadcaster.cs

@@ -14,7 +14,7 @@ public class IrcBroadcaster : IChatBroadcaster
         _encryption = encryption;
     }
 
-    public async Task SendMessageToChannelAsync(string channelName, MessageDto message)
+    public async Task SendMessageToChannelAsync(string channelName, MessageDto message, string? excludeConnectionId = null)
     {
         // Decrypt transport-encrypted content for IRC clients (they can't handle
         // app-layer encryption). E2E room ciphertext ($RC1$) passes through untouched.
@@ -23,8 +23,11 @@ public class IrcBroadcaster : IChatBroadcaster
 
         foreach (var conn in _gateway.GetConnectionsInChannel(channelName))
         {
-            // IRC convention: don't echo sender's own message
-            if (conn.Nickname == message.SenderUsername)
+            // IRC convention: don't echo a message back to the connection that sent it
+            // (its client already displayed it locally). Match by connection id, not
+            // nickname — the same account may also be online via the TUI or a second
+            // IRC client, and those sessions must still receive the message.
+            if (conn.ConnectionId == excludeConnectionId)
                 continue;
 
             foreach (var line in lines)