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

src/ui/readerview.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <QWidget>
+#include <QLabel>
+#include <QTextBrowser>
+#include <QPushButton>
+#include <QVBoxLayout>
+#include <QHBoxLayout>
+#include "core/mailitem.h"
+
+class ReaderView : public QWidget {
+    Q_OBJECT
+
+public:
+    explicit ReaderView(QWidget *parent = nullptr);
+    ~ReaderView() override = default;
+
+    void setMailItem(const MailItem* item);
+
+signals:
+    void replyRequested(const MailItem* item);
+    void forwardRequested(const MailItem* item);
+    void deleteRequested(const MailItem* item);
+
+private:
+    void setupUI();
+
+    QLabel *m_subjectLabel;
+    QLabel *m_fromLabel;
+    QLabel *m_dateLabel;
+    QTextBrowser *m_bodyViewer;
+    
+    QPushButton *m_replyButton;
+    QPushButton *m_forwardButton;
+    QPushButton *m_deleteButton;
+};