feat: context menus on search panel, track info dialog, separate shuffle buttons

- Add right-click context menus to search panel tracks (play, queue,
  favorites, playlist, go to album/artist, track info) and albums
  (open, favorite, go to artist)
- Add "Track info..." dialog showing metadata (title, performer,
  composer, album, quality, hi-res status) — available everywhere:
  playlists, albums, favorites, search results
- Split artist page shuffle into "Shuffle" (popular tracks) and
  "Shuffle All" (deep shuffle across all releases)
- Remove magnifying glass emoji from welcome text

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

src/view/maincontent.cpp

@@ -16,7 +16,7 @@ MainContent::MainContent(QobuzBackend *backend, PlayQueue *queue, QWidget *paren
     m_welcome = new QLabel(
         tr("<h2>Welcome to Qobuz</h2>"
            "<p>Select something from the library on the left to get started,<br>"
-           "or use the search panel (🔍) to find music.</p>"),
+           "or use the search panel to find music.</p>"),
         this);
     m_welcome->setAlignment(Qt::AlignCenter);