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

tests/autostart_manager_test.cpp

@@ -0,0 +1,26 @@
+#include "autostart_manager.h"
+
+#include <QtTest>
+
+class AutoStartManagerTest : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void createsRunAtLoadLaunchAgent();
+};
+
+void AutoStartManagerTest::createsRunAtLoadLaunchAgent()
+{
+    const QString executablePath = "/Applications/Clouck.app/Contents/MacOS/Clouck";
+    const QString contents = AutoStartManager::launchAgentContents(executablePath);
+
+    QVERIFY(contents.contains("<key>ProgramArguments</key>"));
+    QVERIFY(contents.contains(executablePath));
+    QVERIFY(contents.contains("<key>RunAtLoad</key>"));
+    QVERIFY(contents.contains("<true/>"));
+}
+
+QTEST_APPLESS_MAIN(AutoStartManagerTest)
+
+#include "autostart_manager_test.moc"