feat: album/playlist header and playlist ownership filtering

- Add TrackContextHeader widget: shows album art (fetched via NAM),
  title, subtitle (artist/description), and metadata (year · tracks · duration)
  above the track list when an album or playlist is opened
- Hide header for favorite tracks and search results
- Store user ID in AppSettings on login
- Only show "Delete playlist" for playlists the user owns
- "Add to playlist" submenu only lists owned playlists
- "Remove from this playlist" only appears when viewing an owned playlist

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

src/view/trackcontextheader.hpp

@@ -0,0 +1,162 @@
+#pragma once
+
+#include <QWidget>
+#include <QHBoxLayout>
+#include <QVBoxLayout>
+#include <QLabel>
+#include <QFont>
+#include <QPixmap>
+#include <QStringList>
+#include <QJsonObject>
+#include <QJsonArray>
+#include <QNetworkAccessManager>
+#include <QNetworkReply>
+#include <QNetworkRequest>
+#include <QUrl>
+
+/// Header strip shown above the track list when an album or playlist is open.
+/// Displays album art, title, subtitle, and metadata.
+class TrackContextHeader : public QWidget
+{
+public:
+    explicit TrackContextHeader(QWidget *parent = nullptr)
+        : QWidget(parent)
+    {
+        setFixedHeight(140);
+
+        auto *hlay = new QHBoxLayout(this);
+        hlay->setContentsMargins(12, 8, 12, 8);
+        hlay->setSpacing(14);
+
+        m_art = new QLabel(this);
+        m_art->setFixedSize(120, 120);
+        m_art->setScaledContents(true);
+        m_art->setAlignment(Qt::AlignCenter);
+        m_art->setStyleSheet(QStringLiteral("background: #1a1a1a; border-radius: 4px;"));
+        hlay->addWidget(m_art, 0, Qt::AlignVCenter);
+
+        auto *info = new QWidget(this);
+        auto *vlay = new QVBoxLayout(info);
+        vlay->setContentsMargins(0, 0, 0, 0);
+        vlay->setSpacing(4);
+
+        m_title = new QLabel(info);
+        QFont tf = m_title->font();
+        tf.setPointSize(tf.pointSize() + 5);
+        tf.setBold(true);
+        m_title->setFont(tf);
+        m_title->setWordWrap(true);
+        vlay->addWidget(m_title);
+
+        m_subtitle = new QLabel(info);
+        QFont sf = m_subtitle->font();
+        sf.setPointSize(sf.pointSize() + 1);
+        m_subtitle->setFont(sf);
+        m_subtitle->setWordWrap(true);
+        vlay->addWidget(m_subtitle);
+
+        m_meta = new QLabel(info);
+        QPalette mp = m_meta->palette();
+        mp.setColor(QPalette::WindowText, QColor(0xaa, 0xaa, 0xaa));
+        m_meta->setPalette(mp);
+        vlay->addWidget(m_meta);
+
+        vlay->addStretch();
+        hlay->addWidget(info, 1);
+
+        m_nam = new QNetworkAccessManager(this);
+        QObject::connect(m_nam, &QNetworkAccessManager::finished,
+                [this](QNetworkReply *reply) {
+            reply->deleteLater();
+            if (reply->error() != QNetworkReply::NoError)
+                return;
+            QPixmap pix;
+            if (pix.loadFromData(reply->readAll()))
+                m_art->setPixmap(pix);
+        });
+    }
+
+    void setAlbum(const QJsonObject &album)
+    {
+        m_title->setText(album["title"].toString());
+        m_subtitle->setText(album["artist"].toObject()["name"].toString());
+        m_meta->setText(buildAlbumMeta(album));
+        fetchArt(album["image"].toObject());
+        show();
+    }
+
+    void setPlaylist(const QJsonObject &playlist)
+    {
+        m_title->setText(playlist["name"].toString());
+        const QString desc  = playlist["description"].toString();
+        const QString owner = playlist["owner"].toObject()["name"].toString();
+        m_subtitle->setText(desc.isEmpty() ? owner : desc);
+        m_meta->setText(buildPlaylistMeta(playlist));
+
+        const QJsonArray imgs = playlist["image_rectangle"].toArray();
+        if (!imgs.isEmpty())
+            fetchUrl(imgs.first().toString());
+        else
+            m_art->setPixmap(QPixmap());
+
+        show();
+    }
+
+private:
+    void fetchArt(const QJsonObject &img)
+    {
+        QString url = img["large"].toString();
+        if (url.isEmpty()) url = img["small"].toString();
+        fetchUrl(url);
+    }
+
+    void fetchUrl(const QString &url)
+    {
+        if (url.isEmpty()) {
+            m_art->setPixmap(QPixmap());
+            return;
+        }
+        if (url == m_currentArtUrl)
+            return;
+        m_currentArtUrl = url;
+        m_nam->get(QNetworkRequest(QUrl(url)));
+    }
+
+    static QString formatDuration(int totalSecs)
+    {
+        const int h = totalSecs / 3600;
+        const int m = (totalSecs % 3600) / 60;
+        if (h > 0)
+            return QStringLiteral("%1h %2m").arg(h).arg(m);
+        return QStringLiteral("%1 min").arg(m);
+    }
+
+    static QString buildAlbumMeta(const QJsonObject &album)
+    {
+        QStringList parts;
+        const QString year = album["release_date_original"].toString().left(4);
+        if (!year.isEmpty()) parts << year;
+        const int tracks = album["tracks_count"].toInt();
+        if (tracks > 0) parts << QStringLiteral("%1 tracks").arg(tracks);
+        const int dur = static_cast<int>(album["duration"].toDouble());
+        if (dur > 0) parts << formatDuration(dur);
+        return parts.join(QStringLiteral("  ·  "));
+    }
+
+    static QString buildPlaylistMeta(const QJsonObject &playlist)
+    {
+        QStringList parts;
+        const int tracks = playlist["tracks_count"].toInt();
+        if (tracks > 0) parts << QStringLiteral("%1 tracks").arg(tracks);
+        const int dur = static_cast<int>(playlist["duration"].toDouble());
+        if (dur > 0) parts << formatDuration(dur);
+        return parts.join(QStringLiteral("  ·  "));
+    }
+
+    QLabel                *m_art      = nullptr;
+    QLabel                *m_title    = nullptr;
+    QLabel                *m_subtitle = nullptr;
+    QLabel                *m_meta     = nullptr;
+    QNetworkAccessManager *m_nam      = nullptr;
+    QString                m_currentArtUrl;
+};