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/api/client.rs

@@ -258,7 +258,10 @@ impl QobuzClient {
     pub async fn get_artist_page(&self, artist_id: i64) -> Result<Value> {
         let resp = self
             .get_request("artist/page")
-            .query(&[("artist_id", artist_id.to_string())])
+            .query(&[
+                ("artist_id", artist_id.to_string()),
+                ("extra",     "topTracks".to_string()),
+            ])
             .send()
             .await?;
         Self::check_response(resp).await