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

src/services/synchronizer.cpp

@@ -1,6 +1,36 @@
 #include "synchronizer.h"
 
-Synchronizer::Synchronizer(QObject* parent)
+Synchronizer::Synchronizer(QObject *parent)
     : QObject(parent)
 {
+}
+
+QVector<MailItem> Synchronizer::fetchMailItems(const QString &folderId, qint64 sinceUid)
+{
+    Q_UNUSED(folderId);
+    Q_UNUSED(sinceUid);
+    return {};
+}
+
+bool Synchronizer::appendMailItem(const QString &folderId, const MailItem &item)
+{
+    Q_UNUSED(folderId);
+    Q_UNUSED(item);
+    return false;
+}
+
+bool Synchronizer::updateMailItemFlags(const QString &folderId, const QString &itemUid, bool read, bool flagged)
+{
+    Q_UNUSED(folderId);
+    Q_UNUSED(itemUid);
+    Q_UNUSED(read);
+    Q_UNUSED(flagged);
+    return false;
+}
+
+bool Synchronizer::deleteMailItem(const QString &folderId, const QString &itemUid)
+{
+    Q_UNUSED(folderId);
+    Q_UNUSED(itemUid);
+    return false;
 }