feat: show top tracks on artist profile with play/shuffle

- Adds extra=topTracks to artist/page API request
- Embeds a List::Tracks widget at the top of ArtistView showing
  the artist's most popular tracks, with Play and Shuffle buttons
- Bubbles playTrackRequested through MainContent up to MainWindow
- Also adds the viz PCM ring buffer FFI infrastructure (for future
  spectrum widget) to the Rust backend

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rust/src/player/decoder.rs

@@ -1,4 +1,5 @@
 use anyhow::Result;
+use rb::RB;
 use std::io::{self, Read, Seek, SeekFrom};
 use std::sync::{
     atomic::{AtomicBool, Ordering},
@@ -176,8 +177,12 @@ pub fn play_track_inline(
         }
     }
     if audio_output.is_none() {
-        *audio_output = Some(AudioOutput::try_open(sample_rate, channels)?);
+        let mut ao = AudioOutput::try_open(sample_rate, channels)?;
+        ao.set_viz_producer(status.viz_ring.producer());
+        *audio_output = Some(ao);
     }
+    status.viz_sample_rate.store(sample_rate, Ordering::Relaxed);
+    status.viz_channels.store(channels as u32, Ordering::Relaxed);
     let ao = audio_output.as_mut().unwrap();
 
     let mut stopped = false;