Add sweetalert to show styled alert on web bluetooth/socket.io errors

static/js/BLE.js

@@ -115,5 +115,7 @@ function revsToRPM(prevRes, res) {
 btn.addEventListener("click", () =>
   connect({
     onChange: parseCSC,
-  }).catch(console.error)
+  }).catch((err) => {
+    swal("Oops", err, "error");
+  })
 );