fix: use SDK-recommended sort pattern for message ordering

Sort messages by serial using comparison operators as shown in the Chat
SDK documentation, rather than findIndex/splice insertion.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rainbowFi

components/ChatBox.jsx

@@ -17,16 +17,7 @@ export default function ChatBox() {
         if (prevMessages.some((existingMessage) => existingMessage.serial === newMessage.serial)) {
           return prevMessages;
         }
-
-        const index = prevMessages.findIndex((existingMessage) => existingMessage.serial > newMessage.serial);
-
-        const newMessages = [...prevMessages];
-        if (index === -1) {
-          newMessages.push(newMessage);
-        } else {
-          newMessages.splice(index, 0, newMessage);
-        }
-        return newMessages;
+        return [...prevMessages, newMessage].sort((a, b) => (a.serial < b.serial ? -1 : b.serial < a.serial ? 1 : 0));
       });
     },
   });