feat: dual time zones, autostart, tray icon, config relocation, tests

- Dual clock (primary/secondary time zone) with IANA picker, persisted in XML
- AutoStartManager: macOS LaunchAgent (com.clouck.clock, RunAtLoad)
- Tray icon: template image, light/dark adaptation, toggle + quit menu
- ConfigManager: default path moved to QStandardPaths::AppConfigLocation
- Qt Test suite (ConfigManager, AutoStartManager) wired into CTest
- GitHub origin renamed to upstream; private Gitea repo as origin

clock_widget.h

@@ -31,6 +31,8 @@ private slots:
     void changeFontColor();
     void changeBackgroundColor();
     void changeFontSize();
+    void changePrimaryTimeZone();
+    void changeSecondaryTimeZone();
     void resetSettings();
     void quitApplication();
 
@@ -40,8 +42,11 @@ private:
     void loadSettings();
     void saveSettings();
     void updateStyleSheet();
+    void changeTimeZone(bool primaryClock);
+    QString formattedTime(const QString &timeZoneId) const;
 
-    QLabel *m_timeLabel;
+    QLabel *m_primaryTimeLabel;
+    QLabel *m_secondaryTimeLabel;
     QTimer *m_timer;
     QMenu *m_contextMenu;
 
@@ -61,6 +66,8 @@ private:
     QColor m_backgroundColor;
     int m_fontSize;
     bool m_alwaysOnTop;
+    QString m_primaryTimeZoneId;
+    QString m_secondaryTimeZoneId;
 
     // Helper methods
     bool isInResizeArea(const QPoint &pos) const;