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

src/services/mimestorage.h

@@ -0,0 +1,30 @@
+#ifndef MIMESTORAGESERVICE_H
+#define MIMESTORAGESERVICE_H
+
+#include <QObject>
+#include <QString>
+#include <QDir>
+#include <QFile>
+#include "core/mailitem.h"
+
+class MimeStorageService : public QObject
+{
+    Q_OBJECT
+public:
+    explicit MimeStorageService(QObject *parent = nullptr);
+    ~MimeStorageService() override = default;
+
+    QString saveEmlFile(const QString &accountId, const QString &folderId, const MailItem &mail);
+    QString getEmlFilePath(const QString &fileId) const;
+    QByteArray readEmlFile(const QString &fileId) const;
+    bool deleteEmlFile(const QString &fileId);
+
+    QStringList listAttachments(const QString &mailItemId) const;
+    bool saveAttachment(const QString &mailItemId, const QString &fileName, const QByteArray &data);
+
+private:
+    QString storagePath() const;
+    QString ensureDirectory(const QString &path) const;
+};
+
+#endif // MIMESTORAGESERVICE_H