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

@@ -254,6 +254,10 @@ void MailListView::setupUI()
     m_treeView->header()->setSectionResizeMode(EmailTreeModel::ColSubject, QHeaderView::Stretch);
     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);

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);
@@ -320,6 +320,10 @@ 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);
 }