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/dialog/settings.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <QDialog>
+#include <QComboBox>
+#include <QLabel>
+
+class SettingsDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit SettingsDialog(QWidget *parent = nullptr);
+
+private:
+    QComboBox *m_formatBox = nullptr;
+
+    void applyChanges();
+};