feat(slint): wire track context-menu actions (favorite/radio/share/playlist/nav)

Connects the previously-inert track context-menu items now that the
backends exist:

  - Add to library -> add_favorite("track").
  - Go to album / Go to artist -> resolve the track (get_track) to its
    album / performer and navigate there.
  - Create radio -> Qobuz track radio (new get_radio_track core wrapper
    over the existing qbz-qobuz endpoint + playback::play_track_radio).
  - Share Qobuz link -> https://www.qobuz.com/track/{id} to clipboard
    (new arboard dep + share module).
  - Share Song.link -> Odesli (api.song.link) pageUrl resolution to
    clipboard.
  - Add to playlist -> a global picker modal (PlaylistPickerModal +
    PlaylistPickerState/Actions + playlist_picker controller) listing
    the user's playlists; picking one calls add_tracks_to_playlist.

Add to mixtape / Make available offline / Track info stay unwired
(no backend yet).

cc

crates/qbz-core/src/core.rs

@@ -1138,6 +1138,19 @@ impl<A: FrontendAdapter + Send + Sync + 'static> QbzCore<A> {
             .map_err(CoreError::Api)
     }
 
+    /// Qobuz track radio (`/radio/track`).
+    pub async fn get_radio_track(
+        &self,
+        track_id: &str,
+    ) -> Result<qbz_models::RadioResponse, CoreError> {
+        let client = self.client.read().await;
+        let client = client.as_ref().ok_or(CoreError::NotInitialized)?;
+        client
+            .get_radio_track(track_id)
+            .await
+            .map_err(CoreError::Api)
+    }
+
     /// Dynamic mix suggestions (`/dynamic/suggest`) seeded from
     /// recently-listened track ids. Returns the suggested tracks.
     pub async fn get_dynamic_suggest(