fix: use writable \$derived for search inputs, remove unnecessary \$state wrap

- Replace \$state + \$effect pattern with writable \$derived (Svelte 5.25+)
  for all searchValue instances across list pages — cleaner and lint-compliant
- Remove now-unused untrack imports from those files
- Drop \$state() wrapper around SvelteMap in device-mapping-dialog
  (SvelteMap is already reactive)

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

packages/frontend/src/routes/play/components/device-mapping-dialog.svelte

@@ -16,7 +16,7 @@
   let { open, recordedDevices, connectedDevices, onConfirm, onCancel }: Props = $props();
 
   // Device mappings: recorded device name -> connected device
-  let mappings = $state(new SvelteMap<string, BluetoothDevice>());
+  let mappings = new SvelteMap<string, BluetoothDevice>();
 
   // Check if a connected device is compatible with a recorded device
   function isCompatible(recordedDevice: DeviceInfo, connectedDevice: BluetoothDevice): boolean {