A running session can have its claude.ai Project attached or removed

A new set_attached_project command lets the service hosting a session change which claude.ai Project the session uses, without restarting it. It takes a project_uuid, which must be a UUID (a unique project ID) or null:

• a UUID sets CLAUDE_PROJECT_UUID for the session
• null clears it

The command fails with an error if the session does not get its Project through the service hosting it.