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

src/services/folderservice.h

@@ -0,0 +1,24 @@
+#ifndef FOLDERSERVICE_H
+#define FOLDERSERVICE_H
+
+#include <QObject>
+#include <QVector>
+#include "models/folder.h"
+#include "db/dao/folderdao.h"
+
+class FolderService : public QObject
+{
+    Q_OBJECT
+public:
+    explicit FolderService(QObject *parent = nullptr);
+    ~FolderService() override = default;
+
+    QVector<Folder> getFoldersForAccount(const QString &accountId);
+    void refreshFolders(const QString &accountId);
+    Folder getFolderById(const QString &folderId);
+
+signals:
+    void foldersChanged(const QString &accountId);
+};
+
+#endif // FOLDERSERVICE_H