refactor: MainWindow class into multiple items / controllers ; fix: Bug with PlaylistBrowserDialog.cpp : List item "No playlists available" was selectable

src/gui/NowPlayingPanel.h

@@ -0,0 +1,49 @@
+#pragma once
+#include <QGroupBox>
+#include <QLabel>
+#include <QSlider>
+#include <QPushButton>
+#include <QCheckBox>
+
+class CoverArtWidget;
+namespace engine { struct Track; }
+
+class NowPlayingPanel : public QGroupBox
+{
+    Q_OBJECT
+public:
+    explicit NowPlayingPanel(QWidget *parent = nullptr);
+
+    QCheckBox *shuffleCheckBox() const { return m_chkShuffle; }
+    QCheckBox *repeatCheckBox()  const { return m_chkRepeat;  }
+
+public slots:
+    void updateTrack(const engine::Track *track);
+    void updatePosition(qint64 posFrames, qint64 totalFrames, float sampleRate);
+    void setPlaybackActive(bool playing);   
+
+signals:
+    void playPauseClicked();
+    void prevClicked();
+    void nextClicked();
+    void seekRequested(double fraction);   // 0.0–1.0
+    void volumeChanged(int percent);       // 0–100
+
+private:
+    void buildLayout();
+
+    CoverArtWidget *m_cover;
+    QLabel         *m_lblTitle  = new QLabel("No track selected");
+    QLabel         *m_lblArtist = new QLabel(" ");
+    QLabel         *m_lblAlbum  = new QLabel(" ");
+    QLabel         *m_lblTime   = new QLabel("0:00 / 0:00");
+    QSlider        *m_seekBar   = new QSlider(Qt::Horizontal);
+    QPushButton    *m_btnPrev   = new QPushButton("|<");
+    QPushButton    *m_btnPlay   = new QPushButton("Play");
+    QPushButton    *m_btnNext   = new QPushButton(">|");
+    QCheckBox      *m_chkShuffle = new QCheckBox("Shuffle");
+    QCheckBox      *m_chkRepeat  = new QCheckBox("Repeat");
+    QSlider        *m_volSlider  = new QSlider(Qt::Horizontal);
+
+    bool m_seekDragging { false };
+};