feat(settings): add limit_quality_to_device setting

Add new audio setting to limit streaming quality based on device
capabilities. When enabled (default: true), QBZ will avoid requesting
tracks that exceed the device's max supported sample rate.

This ensures bit-perfect playback by preventing the need to resample
high-res tracks on devices that don't support them.

- Add limit_quality_to_device field to AudioSettings
- Add database migration for new column
- Add Tauri command for frontend integration

cc

src-tauri/src/config/audio_settings.rs

@@ -22,6 +22,10 @@ pub struct AudioSettings {
     pub stream_buffer_seconds: u8,
     /// When true, skip L1+L2 cache writes (streaming-only mode). Offline cache still works.
     pub streaming_only: bool,
+    /// When true, limit streaming quality to device's max supported sample rate.
+    /// This ensures bit-perfect playback by avoiding tracks that exceed device capabilities.
+    /// Default: true (recommended for bit-perfect setups)
+    pub limit_quality_to_device: bool,
 }
 
 impl Default for AudioSettings {
@@ -37,6 +41,7 @@ impl Default for AudioSettings {
             stream_first_track: true,  // Enabled by default for faster playback start
             stream_buffer_seconds: 3,  // 3 seconds initial buffer
             streaming_only: false,  // Disabled by default (cache tracks for instant replay)
+            limit_quality_to_device: true,  // Enabled by default for bit-perfect guarantee
         }
     }
 }
@@ -82,6 +87,7 @@ impl AudioSettingsStore {
         let _ = conn.execute("ALTER TABLE audio_settings ADD COLUMN stream_first_track INTEGER DEFAULT 0", []);
         let _ = conn.execute("ALTER TABLE audio_settings ADD COLUMN stream_buffer_seconds INTEGER DEFAULT 3", []);
         let _ = conn.execute("ALTER TABLE audio_settings ADD COLUMN streaming_only INTEGER DEFAULT 0", []);
+        let _ = conn.execute("ALTER TABLE audio_settings ADD COLUMN limit_quality_to_device INTEGER DEFAULT 1", []);
 
         Ok(Self { conn })
     }
@@ -89,7 +95,7 @@ impl AudioSettingsStore {
     pub fn get_settings(&self) -> Result<AudioSettings, String> {
         self.conn
             .query_row(
-                "SELECT output_device, exclusive_mode, dac_passthrough, preferred_sample_rate, backend_type, alsa_plugin, alsa_hardware_volume, stream_first_track, stream_buffer_seconds, streaming_only FROM audio_settings WHERE id = 1",
+                "SELECT output_device, exclusive_mode, dac_passthrough, preferred_sample_rate, backend_type, alsa_plugin, alsa_hardware_volume, stream_first_track, stream_buffer_seconds, streaming_only, limit_quality_to_device FROM audio_settings WHERE id = 1",
                 [],
                 |row| {
                     // Parse backend_type from JSON string
@@ -113,6 +119,7 @@ impl AudioSettingsStore {
                         stream_first_track: row.get::<_, Option<i64>>(7)?.unwrap_or(0) != 0,
                         stream_buffer_seconds: row.get::<_, Option<i64>>(8)?.unwrap_or(3) as u8,
                         streaming_only: row.get::<_, Option<i64>>(9)?.unwrap_or(0) != 0,
+                        limit_quality_to_device: row.get::<_, Option<i64>>(10)?.unwrap_or(1) != 0,
                     })
                 },
             )
@@ -230,6 +237,16 @@ impl AudioSettingsStore {
             .map_err(|e| format!("Failed to set streaming only: {}", e))?;
         Ok(())
     }
+
+    pub fn set_limit_quality_to_device(&self, enabled: bool) -> Result<(), String> {
+        self.conn
+            .execute(
+                "UPDATE audio_settings SET limit_quality_to_device = ?1 WHERE id = 1",
+                params![enabled as i64],
+            )
+            .map_err(|e| format!("Failed to set limit quality to device: {}", e))?;
+        Ok(())
+    }
 }
 
 /// Thread-safe wrapper
@@ -343,3 +360,12 @@ pub fn set_audio_streaming_only(
     let store = state.store.lock().map_err(|e| format!("Lock error: {}", e))?;
     store.set_streaming_only(enabled)
 }
+
+#[tauri::command]
+pub fn set_audio_limit_quality_to_device(
+    state: tauri::State<'_, AudioSettingsState>,
+    enabled: bool,
+) -> Result<(), String> {
+    let store = state.store.lock().map_err(|e| format!("Lock error: {}", e))?;
+    store.set_limit_quality_to_device(enabled)
+}

src-tauri/src/lib.rs

@@ -785,6 +785,7 @@ pub fn run() {
             config::audio_settings::set_audio_stream_first_track,
             config::audio_settings::set_audio_stream_buffer_seconds,
             config::audio_settings::set_audio_streaming_only,
+            config::audio_settings::set_audio_limit_quality_to_device,
             // Audio backend commands
             commands::get_available_backends,
             commands::get_devices_for_backend,