implement all TODO taks

src/main/java/chat/ChatServer.java

@@ -39,20 +39,29 @@ public class ChatServer {
     }
 
     public void broadcast(String message, ClientHandler sender) {
-        // step 1: iterate through connectedClients safely
-        // step 2: skip the sender client
-        // step 3: send message to remaining clients using sendMessage
+
+        synchronized (connectedClients) {
+            for (ClientHandler client : connectedClients) {
+                if (client != sender) {
+                    client.sendMessage(message);
+                }
+            }
+        }
     }
 
     public void broadcastSystemMessage(String message) {
-        // step 1: iterate through all connected clients
-        // step 2: send system message to each client
+
+        synchronized (connectedClients) {
+            for (ClientHandler client : connectedClients) {
+                client.sendMessage(message);
+            }
+        }
     }
 
     public void removeClient(ClientHandler clientHandler) {
-        // step 1: remove client from connectedClients set
-        // step 2: retrieve username from clientHandler
-        // step 3: broadcast system message about user leaving
+
+        connectedClients.remove(clientHandler);
+        broadcastSystemMessage("[System] " + clientHandler.getUsername() + " left the chat.");
     }
 
     public static void main(String[] args) {