Function build_layout 

pub fn build_layout(
    session: &str,
    members: &[MemberInstance],
    layout: &Option<LayoutConfig>,
    project_root: &Path,
    workflow_mode: WorkflowMode,
    orchestrator_pane: bool,
    orchestrator_position: OrchestratorPosition,
) -> Result<HashMap<String, String>>

Build the tmux layout for a team session.

Creates the session with the first member’s pane, then splits to create all remaining panes. Returns a mapping of member name → tmux pane target.