Add VNC-only scale-to-fit vs actual-size display toggle

VNC has no equivalent of RDP's MS-RDPEDISP to request a different
resolution from the guest, so a high-resolution remote desktop
previously always got shrunk to fit the window, making text
illegible. Adds a per-tab "Display Mode" choice (tab-bar right-click)
between the existing scale-to-fit behavior and a new actual-size mode
that renders the framebuffer at its native pixel size inside a
QScrollArea. Reuses VncDisplayWidget's existing scale-to-fit render
math unchanged -- it degenerates to an exact 1:1 mapping once the
widget is fixed to the remote's own size. Persisted like the terminal
theme preference.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/session_tab.cpp

@@ -24,6 +24,7 @@
 #include <QComboBox>
 #include <QProcessEnvironment>
 #include <QPushButton>
+#include <QScrollArea>
 #include <QThread>
 #include <QTimer>
 #include <QToolButton>
@@ -81,6 +82,7 @@ SessionTab::SessionTab(const Profile& profile,
       m_sshTerminal(nullptr),
       m_rdpDisplay(nullptr),
       m_vncDisplay(nullptr),
+      m_vncScrollArea(nullptr),
       m_terminalOutput(nullptr),
       m_eventLog(nullptr),
       m_toggleEventsButton(nullptr),
@@ -102,6 +104,10 @@ SessionTab::SessionTab(const Profile& profile,
 
     setupUi();
 
+    if (m_vncDisplay != nullptr) {
+        m_vncDisplay->setScaleToFit(preferences.vncScaleToFit);
+    }
+
     if (m_useKodoTermForSsh) {
         connect(m_sshTerminal,
                 &KodoTerm::finished,
@@ -457,6 +463,28 @@ bool SessionTab::supportsZoom() const
     return m_useKodoTermForSsh || m_terminalOutput != nullptr;
 }
 
+bool SessionTab::supportsVncScaleToggle() const
+{
+    return m_vncDisplay != nullptr;
+}
+
+void SessionTab::setVncScaleToFit(bool scaleToFit)
+{
+    if (m_vncDisplay == nullptr || m_vncDisplay->scaleToFit() == scaleToFit) {
+        return;
+    }
+
+    m_vncDisplay->setScaleToFit(scaleToFit);
+    appendEvent(scaleToFit ? QStringLiteral("Display mode set to scale to fit.")
+                          : QStringLiteral("Display mode set to actual size."));
+    emit vncScaleModeChanged(scaleToFit);
+}
+
+bool SessionTab::vncScaleToFit() const
+{
+    return m_vncDisplay != nullptr ? m_vncDisplay->scaleToFit() : true;
+}
+
 void SessionTab::zoomIn()
 {
     if (m_useKodoTermForSsh && m_sshTerminal != nullptr) {
@@ -731,7 +759,11 @@ void SessionTab::setupUi()
         rootLayout->addWidget(m_rdpDisplay, 1);
     } else if (m_profile.protocol.compare(QStringLiteral("VNC"), Qt::CaseInsensitive) == 0) {
         m_vncDisplay = new VncDisplayWidget(this);
-        rootLayout->addWidget(m_vncDisplay, 1);
+        m_vncScrollArea = new QScrollArea(this);
+        m_vncScrollArea->setWidget(m_vncDisplay);
+        m_vncScrollArea->setWidgetResizable(true);
+        m_vncScrollArea->setFrameShape(QFrame::NoFrame);
+        rootLayout->addWidget(m_vncScrollArea, 1);
     } else {
         m_terminalOutput = new TerminalView(this);
         QFont fallbackFont = defaultTerminalFont();