fix: clean up stale sorter entries and fix battery reactivity

ButtplugMessageSorter never deleted entries from _waitingMsgs after
resolving, causing unsolicited DeviceList messages (with reused Ids)
to be swallowed. Also fix battery level not updating in UI by accessing
the device through the Svelte $state proxy array.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/play/+page.svelte

@@ -63,10 +63,11 @@ async function onDeviceAdded(dev: ButtplugClientDevice) {
 	const device = convertDevice(dev);
 	devices.push(device);
 
-	// Try to read battery level
+	// Try to read battery level — access through the reactive array so Svelte detects the mutation
+	const idx = devices.length - 1;
 	if (device.hasBattery) {
 		try {
-			device.batteryLevel = await dev.battery();
+			devices[idx].batteryLevel = await dev.battery();
 		} catch (e) {
 			console.warn(`Failed to read battery for ${dev.name}:`, e);
 		}