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/library.cpp

@@ -0,0 +1,110 @@
+#include "library.hpp"
+
+#include <QHeaderView>
+#include <QJsonArray>
+#include <QJsonObject>
+
+namespace List
+{
+
+static constexpr int TypeRole    = Qt::UserRole + 1;
+static constexpr int IdRole      = Qt::UserRole + 2;
+static constexpr int NameRole    = Qt::UserRole + 3;
+
+enum NodeType {
+    NodeFavTracks,
+    NodeFavAlbums,
+    NodeFavArtists,
+    NodePlaylist,
+};
+
+Library::Library(QobuzBackend *backend, QWidget *parent)
+    : QTreeWidget(parent)
+    , m_backend(backend)
+{
+    setHeaderHidden(true);
+    setRootIsDecorated(true);
+    setContextMenuPolicy(Qt::NoContextMenu);
+
+    buildStaticNodes();
+
+    connect(m_backend, &QobuzBackend::userPlaylistsLoaded,
+            this, &Library::onUserPlaylistsLoaded);
+    connect(this, &QTreeWidget::itemClicked,
+            this, &Library::onItemClicked);
+    connect(this, &QTreeWidget::itemDoubleClicked,
+            this, &Library::onItemDoubleClicked);
+}
+
+void Library::buildStaticNodes()
+{
+    // My Library
+    m_myLibNode = new QTreeWidgetItem(this, QStringList{tr("My Library")});
+    m_myLibNode->setExpanded(true);
+
+    auto *tracksItem = new QTreeWidgetItem(m_myLibNode, QStringList{tr("Favorite Tracks")});
+    tracksItem->setData(0, TypeRole, NodeFavTracks);
+
+    auto *albumsItem = new QTreeWidgetItem(m_myLibNode, QStringList{tr("Favorite Albums")});
+    albumsItem->setData(0, TypeRole, NodeFavAlbums);
+
+    auto *artistsItem = new QTreeWidgetItem(m_myLibNode, QStringList{tr("Favorite Artists")});
+    artistsItem->setData(0, TypeRole, NodeFavArtists);
+
+    // Playlists
+    m_playlistsNode = new QTreeWidgetItem(this, QStringList{tr("Playlists")});
+    m_playlistsNode->setExpanded(true);
+}
+
+void Library::refresh()
+{
+    // Remove old playlist children
+    while (m_playlistsNode->childCount() > 0)
+        delete m_playlistsNode->takeChild(0);
+
+    m_backend->getUserPlaylists();
+}
+
+void Library::onUserPlaylistsLoaded(const QJsonObject &result)
+{
+    while (m_playlistsNode->childCount() > 0)
+        delete m_playlistsNode->takeChild(0);
+
+    const QJsonArray items = result["items"].toArray();
+    for (const auto &v : items) {
+        const QJsonObject pl = v.toObject();
+        const QString name   = pl["name"].toString();
+        const qint64  id     = static_cast<qint64>(pl["id"].toDouble());
+
+        auto *item = new QTreeWidgetItem(m_playlistsNode, QStringList{name});
+        item->setData(0, TypeRole, NodePlaylist);
+        item->setData(0, IdRole,   id);
+        item->setData(0, NameRole, name);
+    }
+}
+
+void Library::onItemClicked(QTreeWidgetItem *item, int)
+{
+    if (!item) return;
+    const int type = item->data(0, TypeRole).toInt();
+
+    switch (type) {
+    case NodeFavTracks:  emit favTracksRequested();  break;
+    case NodeFavAlbums:  emit favAlbumsRequested();  break;
+    case NodeFavArtists: emit favArtistsRequested(); break;
+    case NodePlaylist: {
+        const qint64  id   = item->data(0, IdRole).toLongLong();
+        const QString name = item->data(0, NameRole).toString();
+        emit playlistRequested(id, name);
+        break;
+    }
+    default: break;
+    }
+}
+
+void Library::onItemDoubleClicked(QTreeWidgetItem *item, int column)
+{
+    onItemClicked(item, column);
+}
+
+} // namespace List