fix: responsive widths + email selection fix

- MailListView: setMinimumSectionSize(50) + setStretchLastSection(false) to allow header shrinking
- MainMainWindow: reduce folder tree min width 220->160, reader min width 350->280
- Allow splitter children to not be collapsible but shrink freely
- Fix onRowSelected slot signature to match currentRowChanged signal

src/ui/maillistview.cpp

@@ -255,6 +255,10 @@ void MailListView::setupUI()
     m_treeView->header()->setSectionResizeMode(EmailTreeModel::ColSender, QHeaderView::Stretch);
     m_treeView->header()->setSectionResizeMode(EmailTreeModel::ColDate, QHeaderView::ResizeToContents);
     
+    // Allow shrinking by setting minimum section sizes
+    m_treeView->header()->setMinimumSectionSize(50);
+    m_treeView->header()->setStretchLastSection(false);
+
     connect(m_treeView->selectionModel(), &QItemSelectionModel::selectionChanged,
             this, &MailListView::onSelectionChanged);
     // Single-click selection in tree view -> emit emailSelected for reader pane
@@ -572,10 +576,11 @@ void MailListView::onRowsInserted(const QModelIndex &parent, int first, int last
     }
 }
 
-void MailListView::onRowSelected(const QModelIndex &index)
+void MailListView::onRowSelected(const QModelIndex &current, const QModelIndex &previous)
 {
-    if (!index.isValid()) return;
+    Q_UNUSED(previous);
-    QModelIndex proxyIdx = m_proxyModel->mapToSource(index);
+    if (!current.isValid()) return;
+    QModelIndex proxyIdx = m_proxyModel->mapToSource(current);
     if (proxyIdx.isValid() && proxyIdx.data(EmailTreeModel::MailIdRole).isValid()) {
         int mailId = proxyIdx.data(EmailTreeModel::MailIdRole).toInt();
         emit emailSelected(mailId);

src/ui/maillistview.h

@@ -54,7 +54,7 @@ public slots:
     void setFolderType(const QString& folderType); // "inbox", "sent", "drafts", etc.
 
 private slots:
-    void onRowSelected(const QModelIndex &index);
+    void onRowSelected(const QModelIndex &current, const QModelIndex &previous);
     void onSearchTextChanged(const QString &text);
     void onFilterChanged();
     void onGroupByChanged(int index);

src/ui/mainmainwindow.cpp

@@ -224,7 +224,7 @@ void MainMainWindow::setupMailPage()
     m_folderTree = new QTreeView();
     m_folderTree->setHeaderHidden(true);
     m_folderTree->setIndentation(20);
-    m_folderTree->setMinimumWidth(220);
+    m_folderTree->setMinimumWidth(160);  // Reduced from 220
     m_folderTree->setMaximumWidth(350);
     m_folderTree->setFrameShape(QFrame::NoFrame);
     m_folderTree->setExpandsOnDoubleClick(true);
@@ -291,7 +291,7 @@ void MainMainWindow::setupMailPage()
 
     // Reader view
     m_emailViewer = new ReaderView();
-    m_emailViewer->setMinimumWidth(350);
+    m_emailViewer->setMinimumWidth(280);  // Reduced from 350
     connect(m_emailViewer, &ReaderView::replyRequested, this, &MainMainWindow::onReaderReplyRequested);
     connect(m_emailViewer, &ReaderView::forwardRequested, this, &MainMainWindow::onReaderForwardRequested);
     connect(m_emailViewer, &ReaderView::deleteRequested, this, &MainMainWindow::onReaderDeleteRequested);
@@ -321,6 +321,10 @@ void MainMainWindow::setupMailPage()
     // Default sizes: left pane (folders+categories) 300, list 380, viewer flex
     m_folderSplitter->setSizes({300, 380, 600});
     
+    // Allow each pane to shrink further
+    m_folderSplitter->setHandleWidth(1);
+    m_folderSplitter->setChildrenCollapsible(false);
+
     mailLayout->addWidget(m_folderSplitter);
 }