fix: active device highlight incorrect when using default device

- mixer.Init: convert database 'default' to '' for SDL default device
- AudioOptions.Init: fallback to first SDL device when current device is default
  and config stores 'default'

Fixes known issue from changelog.txt

internal/mixer/mixer.go

@@ -64,7 +64,11 @@ func Init(cfg *db.AppConfig, onUpdate func()) error {
 		logger.Error("Failed to initialize MP3/OGG support: %v", err)
 	}
 
-	if err := openDeviceLocked(cfg.SelectedAudioDevice); err != nil {
+	deviceName := cfg.SelectedAudioDevice
+	if deviceName == "default" {
+		deviceName = ""
+	}
+	if err := openDeviceLocked(deviceName); err != nil {
 		sdl.QuitSubSystem(sdl.INIT_AUDIO)
 		return err
 	}

internal/page/AudioOptions.go

@@ -169,12 +169,24 @@ func (p *AudioOptions) Init(ctx *PageCtx) error {
 
 	// Set active device index based on mixer's current device
 	currentName := mixer.CurrentDevice()
+	config, err = db.GetConfig(p.Context.DbPtr)
+	if err != nil {
+		panic(err)
+	}
+	p.activeDeviceIndex = -1 // default to not found
 	for i, dev := range p.AudioDevices {
 		if dev.Label == currentName {
 			p.activeDeviceIndex = i
 			break
 		}
 	}
+	// If not found and current device is default (""), check saved config
+	if p.activeDeviceIndex == -1 && currentName == "" && config.SelectedAudioDevice == "default" {
+		// Default device is selected - first device in SDL list is typically the default
+		if len(p.AudioDevices) > 0 {
+			p.activeDeviceIndex = 0
+		}
+	}
 
 	// Make sure the audio_files table is populated.
 	if err = p.seedAudioFiles(); err != nil {