Initial implementation of qobuz-qt

- Rust backend (qobuz-backend static lib): Qobuz API client (reqwest/tokio),
  Symphonia audio decoder, CPAL audio output, extern "C" FFI bridge
- Qt 6 frontend mirroring spotify-qt layout: toolbar with playback controls,
  left library dock, central track list, right search panel
- Auth: email/password login with MD5-signed requests; session token persisted
  via QSettings
- Playback: double-click a track → Rust fetches stream URL → Symphonia decodes
  → CPAL outputs to default audio device
- Dark Fusion palette matching spotify-qt feel

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

src/list/tracks.hpp

@@ -0,0 +1,40 @@
+#pragma once
+
+#include "../model/tracklistmodel.hpp"
+#include "../backend/qobuzbackend.hpp"
+
+#include <QTreeView>
+#include <QJsonArray>
+#include <QJsonObject>
+
+namespace List
+{
+    /// Track list view — mirrors the spotify-qt List::Tracks widget.
+    /// Displays a flat list of tracks for a playlist, album, search result, etc.
+    class Tracks : public QTreeView
+    {
+        Q_OBJECT
+
+    public:
+        explicit Tracks(QobuzBackend *backend, QWidget *parent = nullptr);
+
+        void loadTracks(const QJsonArray &tracks);
+        void loadAlbum(const QJsonObject &album);
+        void loadPlaylist(const QJsonObject &playlist);
+        void loadSearchTracks(const QJsonArray &tracks);
+
+        void setCurrentTrackId(qint64 id);
+
+    signals:
+        void playTrackRequested(qint64 trackId);
+
+    private:
+        TrackListModel *m_model   = nullptr;
+        QobuzBackend   *m_backend = nullptr;
+        qint64          m_currentTrackId = 0;
+
+        void onDoubleClicked(const QModelIndex &index);
+        void onContextMenu(const QPoint &pos);
+        void resizeColumnsToContent();
+    };
+}