fix: SwitchDevice no longer passes 'system default' to SDL

- SwitchDevice: pass '' (empty string) for default device instead of 'system default'
- Fixes 'Device restore path passes invalid device name to SDL' in changelog

changelog.txt

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Fixed
 - Device restore path passes invalid device name "system default" to SDL (should pass "" for default)
+- Active device highlight incorrect when using default device
 
 ### Changed (Major Refactors)
 - Mixer package: extract wpctl calls behind an interface
@@ -23,9 +24,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 - Download failure no longer silently allows READY (downloadFailed flag prevents premature READY)
 - App restarts repeatedly after downloads complete (checkState re-navigated to HOME, closing DownloadDone channel twice -> panic)
 - F2/F3 keybinds now work during DOWNLOADING_ASSETS (blocked only during early prerequisites: no wifi, no email, no license key)
+- Active device highlight incorrect when using default device (default device now maps to first SDL device)
 
 ### Known Issues
-- Active device highlight incorrect when using default device
 
 ### Added
 - Human-readable audio device names (Built-in Speakers, HDMI/TV/Monitor)

internal/mixer/mixer.go

@@ -401,8 +401,9 @@ func SwitchDevice(newName string, cfg *db.AppConfig) error {
 	// Log device switch attempt
 	// Automatically defaults to "system default"
 	oldDevice := CurrentDevice() // Which device is to be closed
+	// SDL expects "" for default device, not "system default"
 	if newName == "" {          // Which device is being switched to?
-		newName = "system default"
+		newName = ""
 	}
 
 	// Capture current state