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

autostart_manager.cpp

@@ -0,0 +1,79 @@
+#include "autostart_manager.h"
+
+#include <QCoreApplication>
+#include <QDir>
+#include <QFileInfo>
+#include <QSaveFile>
+#include <QStandardPaths>
+#include <QXmlStreamWriter>
+
+namespace
+{
+const QString launchAgentLabel = QStringLiteral("com.clouck.clock");
+}
+
+bool AutoStartManager::enableForCurrentApplication()
+{
+#ifdef Q_OS_MAC
+    const QString agentPath = launchAgentPath();
+    if (agentPath.isEmpty())
+    {
+        return false;
+    }
+
+    const QFileInfo agentFileInfo(agentPath);
+    if (!QDir().mkpath(agentFileInfo.absolutePath()))
+    {
+        return false;
+    }
+
+    QSaveFile agentFile(agentPath);
+    if (!agentFile.open(QIODevice::WriteOnly | QIODevice::Text))
+    {
+        return false;
+    }
+
+    agentFile.write(launchAgentContents(QCoreApplication::applicationFilePath()).toUtf8());
+    return agentFile.commit();
+#else
+    return false;
+#endif
+}
+
+QString AutoStartManager::launchAgentContents(const QString &executablePath)
+{
+    QString contents;
+    QXmlStreamWriter writer(&contents);
+    writer.setAutoFormatting(true);
+    writer.writeStartDocument();
+    writer.writeDTD("<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">");
+    writer.writeStartElement("plist");
+    writer.writeAttribute("version", "1.0");
+    writer.writeStartElement("dict");
+
+    writer.writeTextElement("key", "Label");
+    writer.writeTextElement("string", launchAgentLabel);
+    writer.writeTextElement("key", "ProgramArguments");
+    writer.writeStartElement("array");
+    writer.writeTextElement("string", executablePath);
+    writer.writeEndElement();
+    writer.writeTextElement("key", "RunAtLoad");
+    writer.writeEmptyElement("true");
+
+    writer.writeEndElement();
+    writer.writeEndElement();
+    writer.writeEndDocument();
+
+    return contents;
+}
+
+QString AutoStartManager::launchAgentPath()
+{
+    const QString homePath = QStandardPaths::writableLocation(QStandardPaths::HomeLocation);
+    if (homePath.isEmpty())
+    {
+        return QString();
+    }
+
+    return QDir(homePath).filePath("Library/LaunchAgents/" + launchAgentLabel + ".plist");
+}