feat: Wino-style compact mail view with display modes + hover actions

- CompactMailDelegate: 3 display modes (Compact/Medium/Spacious) like WinUI original
  * Compact: 64px, minimal, no preview
  * Medium: 96px, with preview, detailed categories
  * Spacious: 120px, full padding, preview visible
- Hover actions: Reply (↩), Forward (↪), Mark unread (✎) on right side
- Unread dot indicator (top-right, blue) like WinUI
- User-configurable display mode via combo box in filter bar
- MainMainWindow handlers for reply/forward/mark-unread from compact view
- Signals: replyRequested, forwardRequested, markUnreadRequested

src/ui/mainmainwindow.cpp

@@ -261,6 +261,9 @@ void MainMainWindow::setupMailPage()
     connect(m_mailListView, &MailListView::deleteRequested, this, &MainMainWindow::onDeleteRequested);
     connect(m_mailListView, &MailListView::categoryRequested, this, &MainMainWindow::onCategoryRequested);
     connect(m_mailListView, &MailListView::moreRequested, this, &MainMainWindow::onMoreRequested);
+    connect(m_mailListView, &MailListView::replyRequested, this, &MainMainWindow::onReplyRequested);
+    connect(m_mailListView, &MailListView::forwardRequested, this, &MainMainWindow::onForwardRequested);
+    connect(m_mailListView, &MailListView::markUnreadRequested, this, &MainMainWindow::onMarkUnreadRequested);
     m_folderSplitter->addWidget(m_mailListView);
 
     // Viewer stack: placeholder, reader, compose
@@ -525,6 +528,30 @@ void MainMainWindow::onMoreRequested(int mailId, const QPoint &globalPos)
     menu.exec(globalPos);
 }
 
+void MainMainWindow::onReplyRequested(int mailId)
+{
+    onReaderReplyRequested(mailId);
+}
+
+void MainMainWindow::onForwardRequested(int mailId)
+{
+    onReaderForwardRequested(mailId);
+}
+
+void MainMainWindow::onMarkUnreadRequested(int mailId)
+{
+    auto item = MailItemDao::findById(mailId);
+    if (item.has_value()) {
+        item->setRead(false);
+        MailItemDao::update(*item);
+        m_emailModel->refresh();
+        if (m_currentMailId == mailId) {
+            m_emailViewer->setMailItem(&*item);
+        }
+        statusBar()->showMessage(tr("Marcado como no leído"), 2000);
+    }
+}
+
 void MainMainWindow::onNewMessage()
 {    // Show compose view in the viewer stack
     m_embeddedComposeView->initializeComposition();