Fix ALSA device filtering and quality badge hardware sample rate

Problem 1: ALSA backend showed only 1 device or listed plugins/virtual devices
that don't work for playback (null, lavrate, samplerate, etc.).

Solution: Filter aplay -L output to only include actual playback devices:
- Hardware devices (hw:, plughw:, sysdefault:CARD=, front:CARD=)
- System defaults (default, pipewire, pulse)
- Digital outputs (hdmi:, iec958:, surround)

Problem 2: Quality badge showed file sample rate (e.g., 44.1kHz) instead of
actual hardware sample rate (e.g., 192kHz) when DAC Passthrough was active.

Solution: ExpandedPlayer now polls hardware_sample_rate every second when
DAC Passthrough is enabled and displays the real hardware rate instead of
the file metadata rate.

Changes:
- alsa_backend.rs: Add is_valid_device() filter for playback devices
- ExpandedPlayer.svelte: Poll get_hardware_audio_status every 1s
- ExpandedPlayer.svelte: Use displaySamplingRate (hardware rate when DAC on)

This ensures the quality badge accurately reflects bit-perfect playback status.

src-tauri/src/audio/alsa_backend.rs

@@ -44,11 +44,11 @@ impl AlsaBackend {
         Ok(Self { host })
     }
 
-    /// Enumerate ALSA devices using aplay -L for complete device list
+    /// Enumerate ALSA devices using aplay -L, filtering only playback devices
     fn enumerate_alsa_devices(&self) -> BackendResult<Vec<AudioDevice>> {
         let mut devices = Vec::new();
 
-        // Use aplay -L to get all ALSA device names (including virtual devices)
+        // Use aplay -L to get all ALSA device names
         let output = Command::new("aplay")
             .arg("-L")
             .output()
@@ -62,12 +62,27 @@ impl AlsaBackend {
         let mut current_device: Option<String> = None;
         let mut current_description: Option<String> = None;
 
+        // Helper to check if device is valid for playback
+        let is_valid_device = |id: &str| -> bool {
+            // Only include actual hardware devices and useful virtual devices
+            id == "default"
+                || id == "pipewire"
+                || id == "pulse"
+                || id.starts_with("hw:")
+                || id.starts_with("plughw:")
+                || id.starts_with("sysdefault:CARD=")
+                || id.starts_with("default:CARD=")
+                || id.starts_with("front:CARD=")
+                || id.starts_with("surround")
+                || id.starts_with("hdmi:")
+                || id.starts_with("iec958:")
+        };
+
         for line in stdout.lines() {
             if line.is_empty() {
                 // Empty line marks end of device entry
                 if let (Some(id), Some(desc)) = (current_device.take(), current_description.take()) {
-                    // Skip null device
-                    if id != "null" {
+                    if is_valid_device(&id) {
                         let is_default = id == "default";
                         devices.push(AudioDevice {
                             id: id.clone(),
@@ -90,7 +105,7 @@ impl AlsaBackend {
 
         // Don't forget last device
         if let (Some(id), Some(desc)) = (current_device, current_description) {
-            if id != "null" {
+            if is_valid_device(&id) {
                 let is_default = id == "default";
                 devices.push(AudioDevice {
                     id: id.clone(),
@@ -102,7 +117,7 @@ impl AlsaBackend {
             }
         }
 
-        log::info!("[ALSA Backend] Enumerated {} devices via aplay -L", devices.len());
+        log::info!("[ALSA Backend] Enumerated {} devices via aplay -L (filtered)", devices.len());
         for (idx, dev) in devices.iter().enumerate() {
             log::info!("  [{}] {} - {}", idx, dev.name, dev.description.as_deref().unwrap_or(""));
         }

src/lib/components/ExpandedPlayer.svelte

@@ -1,9 +1,20 @@
 <script lang="ts">
+  import { invoke } from '@tauri-apps/api/core';
   import { X, Shuffle, SkipBack, Play, Pause, SkipForward, Repeat, Heart, List, Maximize2, MoreHorizontal, Cast } from 'lucide-svelte';
   import QualityBadge from './QualityBadge.svelte';
   import LyricsLines from './lyrics/LyricsLines.svelte';
   import { startActiveLineUpdates } from '$lib/stores/lyricsStore';
 
+  interface HardwareAudioStatus {
+    hardware_sample_rate: number | null;
+    hardware_format: string | null;
+    is_active: boolean;
+  }
+
+  interface AudioSettings {
+    dac_passthrough: boolean;
+  }
+
   interface LyricsLine {
     text: string;
   }
@@ -89,10 +100,47 @@
   let volumeRef: HTMLDivElement | null = $state(null);
   let isDraggingProgress = $state(false);
   let isDraggingVolume = $state(false);
+  let hardwareSampleRate = $state<number | null>(null);
+  let dacPassthrough = $state(false);
 
   const progress = $derived((currentTime / duration) * 100 || 0);
   const hasLyrics = $derived(lyricsLines.length > 0);
 
+  // Use hardware sample rate when DAC passthrough is active, otherwise use track sample rate
+  const displaySamplingRate = $derived(
+    dacPassthrough && hardwareSampleRate
+      ? hardwareSampleRate / 1000  // Convert Hz to kHz
+      : samplingRate
+  );
+
+  // Poll hardware sample rate when DAC passthrough is active
+  $effect(() => {
+    if (!isOpen) return;
+
+    async function loadStatus() {
+      try {
+        const [settings, hwStatus] = await Promise.all([
+          invoke<AudioSettings>('get_audio_settings'),
+          invoke<HardwareAudioStatus>('get_hardware_audio_status').catch(() => null)
+        ]);
+        dacPassthrough = settings.dac_passthrough;
+        hardwareSampleRate = hwStatus?.hardware_sample_rate ?? null;
+      } catch (err) {
+        console.error('Failed to load audio status:', err);
+      }
+    }
+
+    loadStatus();
+
+    const pollInterval = setInterval(() => {
+      if (dacPassthrough) {
+        loadStatus();
+      }
+    }, 1000); // Poll every second when DAC passthrough is active
+
+    return () => clearInterval(pollInterval);
+  });
+
   // Ensure lyrics updates run when ExpandedPlayer is open with synced lyrics
   $effect(() => {
     if (isOpen && isPlaying && lyricsSynced) {
@@ -200,7 +248,7 @@
           <h2 class="artist">{artist}</h2>
           <h3 class="album">{album}</h3>
           <div class="quality-info">
-            <QualityBadge {quality} {bitDepth} {samplingRate} />
+            <QualityBadge {quality} {bitDepth} samplingRate={displaySamplingRate} />
           </div>
         </div>