fix: HiFi Wizard now detects real DAC sample rates from /proc/asound

v2_query_dac_capabilities was returning hardcoded sample rates
(44.1-192kHz including 176.4kHz) instead of querying the actual
hardware. This caused incorrect configuration for DACs that don't
support all rates (e.g. DacMagic Plus doesn't support 176.4kHz).

Now queries /proc/asound/cardN/stream0 via PipeWire sink mapping
or ALSA device ID to get the real discrete rates from the USB
descriptor. Falls back to defaults only if detection fails.

cc

crates/qbz-audio/src/pipewire_backend.rs

@@ -79,7 +79,7 @@ impl PipeWireBackend {
 
     /// Query the DAC's supported sample rates from /proc/asound/cardN/stream0.
     /// Returns None if rates can't be determined (non-USB device, continuous range, etc.)
-    fn get_sink_supported_rates(sink_name: &str) -> Option<Vec<u32>> {
+    pub fn get_sink_supported_rates(sink_name: &str) -> Option<Vec<u32>> {
         let alsa_card = Self::get_alsa_card_for_sink(sink_name)?;
 
         let stream_path = format!("/proc/asound/card{}/stream0", alsa_card);