[Feature] Implement real-time collaboration for shared workspaces

As a team member, I want to see who's online and what they're typing in shared workspaces, so that we can collaborate on AI conversations without conflicts or duplication.

As a user, I want to see when teammates are active and typing, so that I know who's working in the workspace and can coordinate effectively.

As a team member, I want to see messages and changes instantly as they happen, so that our team can have fluid, real-time AI collaboration.