chatroom ID

We need unique IDs for the chatrooms currently in use. These IDs must be:

- Created when a new chatroom is created.
- Retrieved for a new client connection.
- Sent along with the message typed by a user.
- Sent along with the response from the server to update the correct chat box.

Trace the chatroom creation, new client connection, and client/server message paths described in the issue. Done means each active chatroom has a unique ID, new connections can retrieve it, and both user messages and server responses carry it so the correct chat box is updated.

Written by the indexing model from the issue text.