feat: artist portrait, race condition fix, and uniform button styling

- Load artist portrait from images.portrait.hash via QNetworkAccessManager
- Fix race condition: fire getArtistReleases after setArtist() clears sections,
  not before (from onArtistLoaded instead of onSearchArtistSelected)
- Apply uniform gold (#FFB232) play/shuffle button style matching album view
- Make biography scrollable (QTextEdit with max height + scroll on overflow)
- Extend track artist name parsing to handle top_tracks {display:...} format

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

src/mainwindow.cpp

@@ -335,6 +335,12 @@ void MainWindow::onAlbumLoaded(const QJsonObject &album)
 void MainWindow::onArtistLoaded(const QJsonObject &artist)
 {
     m_content->showArtist(artist);
+    // Fire release requests only after the artist page is shown — avoids the
+    // race where a fast-responding release request arrives before setArtist()
+    // clears the sections, causing setArtist() to wipe out the data.
+    const qint64 artistId = static_cast<qint64>(artist["id"].toDouble());
+    for (const char *type : {"album", "epSingle", "live", "compilation"})
+        m_backend->getArtistReleases(artistId, QString::fromLatin1(type));
     statusBar()->showMessage(
         tr("Artist: %1").arg(artist["name"].toObject()["display"].toString()), 4000);
 }
@@ -360,9 +366,6 @@ void MainWindow::onSearchAlbumSelected(const QString &albumId)
 void MainWindow::onSearchArtistSelected(qint64 artistId)
 {
     m_backend->getArtist(artistId);
-    // Fire release-type requests in parallel — each updates its section when it arrives
-    for (const char *type : {"album", "epSingle", "live", "compilation"})
-        m_backend->getArtistReleases(artistId, QString::fromLatin1(type));
     statusBar()->showMessage(tr("Loading artist…"));
 }