Subscribes to events scoped to a single project.

Note that every project-scoped LiveView subscribes here via LightningWeb.Hooks.on_mount(:project_scope, ...), as do LightningWeb.WorkflowChannel, LightningWeb.AiAssistantChannel and LightningWeb.RunChannel at join. Anything broadcast on this topic reaches all of them, so new event types must be handled (or explicitly halted) in LightningWeb.Hooks.handle_project_user_event/2 and named in each channel's ignore clause.

Keep this topic quiet. It exists so that a session can be told its own standing changed, and every subscriber is woken for every message on it — a frequent event does not belong here.