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

config_manager.h

@@ -16,11 +16,13 @@ class ConfigManager : public QObject
 public:
     explicit ConfigManager(QObject *parent = nullptr);
 
+    static QString defaultSettingsPath();
+
     // Load settings from XML file
-    bool loadSettings(const QString &filename = "config.xml");
+    bool loadSettings(const QString &filename = QString());
 
     // Save settings to XML file
-    bool saveSettings(const QString &filename = "config.xml");
+    bool saveSettings(const QString &filename = QString());
 
     // Getters
     QColor fontColor() const { return m_fontColor; }
@@ -29,6 +31,8 @@ public:
     bool alwaysOnTop() const { return m_alwaysOnTop; }
     QPoint windowPosition() const { return m_windowPosition; }
     QSize windowSize() const { return m_windowSize; }
+    QString primaryTimeZoneId() const { return m_primaryTimeZoneId; }
+    QString secondaryTimeZoneId() const { return m_secondaryTimeZoneId; }
 
     // Setters
     void setFontColor(const QColor &color) { m_fontColor = color; }
@@ -37,12 +41,14 @@ public:
     void setAlwaysOnTop(bool onTop) { m_alwaysOnTop = onTop; }
     void setWindowPosition(const QPoint &pos) { m_windowPosition = pos; }
     void setWindowSize(const QSize &size) { m_windowSize = size; }
+    void setPrimaryTimeZoneId(const QString &timeZoneId) { m_primaryTimeZoneId = timeZoneId; }
+    void setSecondaryTimeZoneId(const QString &timeZoneId) { m_secondaryTimeZoneId = timeZoneId; }
 
     // Reset to default values
     void resetToDefaults();
 
     // Check if config file exists
-    bool configExists(const QString &filename = "config.xml") const;
+    bool configExists(const QString &filename = QString()) const;
 
 private:
     // Default values
@@ -55,6 +61,8 @@ private:
     bool m_alwaysOnTop;
     QPoint m_windowPosition;
     QSize m_windowSize;
+    QString m_primaryTimeZoneId;
+    QString m_secondaryTimeZoneId;
 };
 
 #endif // CONFIG_MANAGER_H