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

include/changetype.h

@@ -0,0 +1,40 @@
+// changetype.h
+#ifndef CHANGETYPE_H
+#define CHANGETYPE_H
+
+#include "eventbus.h"
+#include <QString>
+#include <QDateTime>
+
+enum ChangeType {
+    ADD,
+    DELETE,
+    UPDATE
+};
+
+struct MailChange {
+    QString mailItemId;
+    QString type; // ADD, DELETE, UPDATE
+    QString subject;
+    QString body;
+    QDateTime timestamp;
+    QString changeSource; // e.g., "IMAP_SYNC", "SMTP_SYNC"
+};
+
+class ChangeProcessor : public QObject {
+    Q_OBJECT
+public:
+    explicit ChangeProcessor(EventBus* bus, QObject *parent = nullptr);
+
+    void processChange(const MailChange& change);
+
+signals:
+    void mailChangeDetected(const MailChange& change);
+
+private:
+    EventBus* m_eventBus;
+    // In a real system, this would interface with the database/DAO layer.
+    void applyChangeToModel(const MailChange& change); 
+};
+
+#endif // CHANGETYPE_H