refactor(v2): migrate get_pipewire_sinks to v2

Path C: legacy CPAL output-sink enumeration was inlined directly in
commands/playback.rs (cfg-gated Linux + non-Linux variants), with
no equivalent in any domain crate. Extract a domain function
`qbz_audio::output_sinks::list_output_sinks` that returns the same
{name, description, volume, is_default} shape (mirrored as the new
public `OutputSinkInfo` struct) for both Linux and non-Linux
platforms, preserving the original logging cadence and the rule
that name == CPAL device name (so saved IDs reopen correctly).

Add v2_get_pipewire_sinks in commands_v2/audio.rs that calls into
qbz_audio directly — no `crate::commands::*` delegation. Updates the
two frontend call sites (AudioOutputBadges.loadStatus and
SettingsView.loadAudioDevices). Legacy command in
commands/playback.rs is preserved untouched; the audio-protected
files (pipewire_backend.rs, audio_settings.rs, player init_device)
are not modified.

cc

src-tauri/src/commands_v2/audio.rs

@@ -43,6 +43,18 @@ pub async fn v2_get_audio_output_status(
     })
 }
 
+/// List the available CPAL output sinks (V2).
+///
+/// Delegates enumeration to `qbz_audio::output_sinks::list_output_sinks`,
+/// which returns the same `{name, description, volume, is_default}` shape
+/// the legacy `get_pipewire_sinks` command returned. Used by the audio
+/// settings UI and AudioOutputBadges to populate the device picker and
+/// label the currently-routed sink.
+#[tauri::command]
+pub fn v2_get_pipewire_sinks() -> Result<Vec<qbz_audio::OutputSinkInfo>, RuntimeError> {
+    qbz_audio::list_output_sinks().map_err(RuntimeError::Internal)
+}
+
 /// Snapshot the presence of the user's currently-selected output
 /// device. Frontend calls this on demand (e.g. when a
 /// `audio:device-missing` toast button fires Retry).

src-tauri/src/lib.rs

@@ -1732,6 +1732,7 @@ pub fn run() {
             commands_v2::v2_reinit_audio_device,
             commands_v2::v2_check_audio_device_presence,
             commands_v2::v2_get_audio_output_status,
+            commands_v2::v2_get_pipewire_sinks,
             commands_v2::v2_get_audio_settings,
             commands_v2::v2_set_audio_output_device,
             commands_v2::v2_set_audio_exclusive_mode,