Function spawn 

pub fn spawn(
    rx: Receiver<TaskEvent>,
    backend: Arc<dyn ExternalBackend>,
    tmux: Arc<TmuxManager>,
    runner: Arc<TaskRunner>,
    capture: Arc<CaptureService>,
    semaphore: Arc<Semaphore>,
    task_manager: Arc<TaskManager>,
    weight_tx: Sender<WeightSignal>,
    router_arc: Arc<RwLock<Router>>,
    dispatching: Arc<DashMap<String, String>>,
    store: Arc<TaskStore>,
    repo: String,
)

Spawn a task that listens for Routed events and dispatches agents.

This mirrors the logic in tick_dispatch_tasks but triggers instantly instead of waiting for the next tick. The dispatching set prevents double-dispatch if the tick loop picks up the same task.