Temporarily disable ALSA Direct backend from UI

ALSA Direct is currently non-functional due to CPAL limitations:
- CPAL cannot enumerate or open hw:X,Y devices required for bit-perfect playback
- Only named devices (front:, iec958:, sysdefault:) work, but they all use ALSA plugins with resampling
- User's DAC cannot achieve bit-perfect playback (stuck at 44.1kHz regardless of track sample rate)

Changes:
- Filter out ALSA Direct from backend selector dropdown
- Auto-switch users from ALSA Direct to Auto on settings load
- Add comments indicating this is temporary until alsa-rs rewrite

This prevents user frustration with a broken backend while we evaluate implementing
direct ALSA support via alsa-rs (bypassing CPAL entirely).

src/lib/components/views/SettingsView.svelte

@@ -214,7 +214,8 @@
   let isLoadingDevices = $state(false);
 
   // Backend selector options (derived)
-  let backendOptions = $derived(['Auto', ...availableBackends.filter(b => b.is_available).map(b => b.name)]);
+  // TEMPORARILY hide ALSA Direct until hw: device support is implemented with alsa-rs
+  let backendOptions = $derived(['Auto', ...availableBackends.filter(b => b.is_available && b.name !== 'ALSA Direct').map(b => b.name)]);
 
   // Helper to check if a device name looks like raw ALSA (needs translation)
   function needsTranslation(name: string): boolean {
@@ -813,8 +814,19 @@
       // Load backend and plugin settings
       if (settings.backend_type) {
         const backend = availableBackends.find(b => b.backend_type === settings.backend_type);
-        selectedBackend = backend?.name ?? 'Auto';
+        const backendName = backend?.name ?? 'Auto';
 
+        // TEMPORARILY: If user had ALSA Direct selected, switch to Auto
+        // (ALSA Direct is temporarily disabled until hw: device support is implemented with alsa-rs)
+        if (backendName === 'ALSA Direct') {
+          selectedBackend = 'Auto';
+          // Switch backend to Auto in backend
+          await invoke('set_audio_backend_type', { backendType: null });
+          console.log('[Audio] Switched from ALSA Direct to Auto (ALSA Direct temporarily disabled)');
+          // Don't load devices for ALSA backend
+          backendDevices = [];
+        } else {
+          selectedBackend = backendName;
           // Load devices for selected backend
           await loadBackendDevices(settings.backend_type);
 
@@ -830,6 +842,7 @@
               outputDevice = 'System Default';
             }
           }
+        }
       } else {
         selectedBackend = 'Auto';
         // Auto mode: always use System Default (no device selection)