Refactor device management and add pending device handling

- Removed unused noDevicesConnected() method and updated its logic.
- Introduced DevicePendingWidget and DevicePendingSidebarItem for better UI handling of pending devices.
- Updated DeviceManagerWidget to manage pending and paired devices more effectively.
- Added LoadingSpinnerWidget for visual feedback during device pairing.

src/loadingspinnerwidget.cpp

@@ -0,0 +1,43 @@
+#include "loadingspinnerwidget.h"
+#include <QPainter>
+
+LoadingSpinnerWidget::LoadingSpinnerWidget(QWidget *parent)
+    : QWidget(parent), m_angle(0), m_color(Qt::gray)
+{
+    connect(&m_timer, &QTimer::timeout, this,
+            &LoadingSpinnerWidget::updateRotation);
+    m_timer.setInterval(15); // Update every 15ms for smooth animation
+    m_timer.start();
+    setFixedSize(24, 24); // Default size
+}
+
+void LoadingSpinnerWidget::setColor(const QColor &color)
+{
+    m_color = color;
+    update(); // Trigger a repaint with the new color
+}
+
+void LoadingSpinnerWidget::paintEvent(QPaintEvent *event)
+{
+    Q_UNUSED(event);
+    QPainter painter(this);
+    painter.setRenderHint(QPainter::Antialiasing);
+
+    int penWidth = 2;
+    QRectF rect(penWidth / 2.0, penWidth / 2.0, width() - penWidth,
+                height() - penWidth);
+
+    QPen pen(m_color);
+    pen.setWidth(penWidth);
+    pen.setCapStyle(Qt::RoundCap);
+    painter.setPen(pen);
+
+    // Draw a 270-degree arc, rotating the start angle
+    painter.drawArc(rect, m_angle * 16, 270 * 16);
+}
+
+void LoadingSpinnerWidget::updateRotation()
+{
+    m_angle = (m_angle + 10) % 360;
+    update(); // Schedule a repaint
+}