feat(dashboard): extract inline script to standalone dashboard.ts/js, add UI build/check recipes, and add route unit tests

stub/src/main.rs

@@ -139,13 +139,11 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 
                     tokio::select! {
                         _ = shutdown_rx.recv() => {
-                            tokio::time::sleep(tokio::time::Duration::from_millis(50)).await;
                             tracing::info!("Shutdown received while connected");
                             break;
                         }
                         _ = &mut send_task => {
                             tracing::error!("Send task exited");
-                            tokio::time::sleep(tokio::time::Duration::from_millis(50)).await;
                             recv_task.abort();
                         }
                         _ = &mut recv_task => {