feat: artist sections, fav indicator, art scaling fix, volume popup fix

- Artist profile: collapsible Albums / EPs & Singles / Other sections
  keyed on release_type; fetches up to 200 albums per artist
- Favorites: starred icon on favorited tracks, context menu shows
  Add or Remove (not both); IDs cached when fav tracks are loaded
- Shuffle button: one-time shuffle via shuffleNow() without touching
  global shuffle flag, so double-click still plays in order
- Now-playing art: replaced setFixedHeight hack with ArtWidget that
  overrides hasHeightForWidth() — scales smoothly up and down, no min-size
- Volume popup: replaced QMenu (laggy, broken drag) with Qt::Popup QFrame;
  appears below button; fixed size locked at 100% label width

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

rust/src/api/models.rs

@@ -98,6 +98,7 @@ pub struct AlbumDto {
     pub maximum_sampling_rate: Option<f64>,
     pub hires_streamable: Option<bool>,
     pub streamable: Option<bool>,
+    pub release_type: Option<String>,
     pub tracks: Option<TracksWrapper>,
 }