[interactive-drive] Add multiplayer support

[wlewNV]

Summary

Allow multiple users to connect to the same interactive-drive session at once, sharing one world-model instance.

The scoping of this issue is intentionally large but will mostly be used to track current ideas / thoughts about having multi-user interaction.

Proposed scope

• Support multiple concurrent client connections to one running session.
• Define how control is shared (e.g. one active driver + spectators, or per-client vehicles).
• Broadcast generated frames to all connected clients.

[jarcherNV]

This is still a valid feature idea, but it is a larger design/architecture item rather than something we are actively prioritizing. Keeping this in the backlog for now.