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/maillistview.cpp

@@ -70,6 +70,22 @@ void MailListView::setupUI()
 
     filterLayout->addStretch();
 
+    // Display mode combo (Compact/Medium/Spacious)
+    m_displayModeCombo = new QComboBox();
+    m_displayModeCombo->addItem("Compacto");
+    m_displayModeCombo->addItem("Medio");
+    m_displayModeCombo->addItem("Espacioso");
+    m_displayModeCombo->setFixedWidth(120);
+    m_displayModeCombo->setStyleSheet(
+        "QComboBox { border: 1px solid #d1d1d6; border-radius: 4px; padding: 4px 8px; "
+        "background: white; min-height: 20px; }"
+        "QComboBox:hover { border-color: #bdbdbd; }"
+        "QComboBox:focus { border-color: #1976D2; }"
+    );
+    connect(m_displayModeCombo, QOverload<int>::of(&QComboBox::currentIndexChanged),
+            this, &MailListView::onDisplayModeChanged);
+    filterLayout->addWidget(m_displayModeCombo);
+
     // Group by combo
     m_groupByCombo = new QComboBox();
     m_groupByCombo->addItem("Sin agrupación");
@@ -282,4 +298,26 @@ void MailListView::onCompactMoreRequested(int mailId, const QPoint &globalPos)
 void MailListView::onCompactMailClicked(int mailId)
 {
     emit emailSelected(mailId);
+}
+
+void MailListView::onCompactReplyRequested(int mailId)
+{
+    emit replyRequested(mailId);
+}
+
+void MailListView::onCompactForwardRequested(int mailId)
+{
+    emit forwardRequested(mailId);
+}
+
+void MailListView::onCompactMarkUnreadRequested(int mailId)
+{
+    emit markUnreadRequested(mailId);
+}
+
+void MailListView::onDisplayModeChanged(int index)
+{
+    CompactMailDelegate::DisplayMode mode = static_cast<CompactMailDelegate::DisplayMode>(index);
+    m_compactDelegate->setDisplayMode(mode);
+    m_listView->update();
 }