add battery voltage to /display so you can see voltages of batteries on the /display page by looking at /display to see the voltages of the batteries on the roombas in case you want to see the battery voltages!! yay!!!!

webui/src/context/telemetryViews.js

@@ -7,6 +7,7 @@ import { shallowArrayEqual, shallowObjectEqual } from './TelemetryContext.jsx';
 const EMPTY_BATTERY_TELEMETRY = Object.freeze({
   batteryChargeMah: null,
   batteryCapacityMah: null,
+  batteryVoltage: null,
 });
 
 const EMPTY_DOCK_TELEMETRY = Object.freeze({
@@ -89,6 +90,7 @@ export function selectBatteryTelemetry(frame) {
   return {
     batteryChargeMah: sensors.batteryChargeMah ?? null,
     batteryCapacityMah: sensors.batteryCapacityMah ?? null,
+    batteryVoltage: (sensors.voltageMv/1000).toPrecision(4) ?? null,
   };
 }