Fix build: synchronize Request API, fix GmailSynchronizer, and migrate UI to Qt6 Widgets

include/gmailauthenticator.h

@@ -0,0 +1,20 @@
+// gmailauthenticator.h
+#ifndef GMAILAUTHENTICATOR_H
+#define GMAILAUTHENTICATOR_H
+
+#include "authenticator.h"
+#include "request.h"
+#include <QString>
+
+class GmailAuthenticator : public IAuthenticator {
+public:
+    GmailAuthenticator(EventBus* bus);
+    bool authenticate(const QString& username, const QString& password, const QString& scope = "email");
+
+private:
+    EventBus* m_eventBus;
+    // Placeholder for actual OAuth flow management
+    bool performOAuth2Flow(const QString& authCode);
+};
+
+#endif // GMAILAUTHENTICATOR_H