Add VNC remote cursor shape sync

Implements RFB's Cursor pseudo-encoding (RFC 6143 SS7.8.2, type -239):
a FramebufferUpdate rectangle carrying a cursor shape instead of
screen content (x/y are the hotspot, not position; width/height are
the cursor image size), decoded into an ARGB32 QImage using the
rectangle's RGB pixel data plus its opacity bitmask, then never
painted into the framebuffer. A 0x0 rectangle means "hide the
cursor" per spec.

VncDisplayWidget gains RdpDisplayWidget's setCursorImage/Hidden/
Default() + applyCursor() shape, reusing its own renderRect()/
effectiveRemoteSize() so cursor scaling works correctly in both the
scale-to-fit and actual-size display modes with no special-casing.
VNC never emits cursorReset() (RFB's Cursor pseudo-encoding has no
"reset to system default" signal, unlike RDP's SetDefault callback) --
setCursorDefault() exists for symmetry but is unused today.

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

src/vnc_display_widget.h

@@ -2,6 +2,7 @@
 #define ORBITHUB_VNC_DISPLAY_WIDGET_H
 
 #include <QImage>
+#include <QPoint>
 #include <QWidget>
 
 class QKeyEvent;
@@ -12,8 +13,7 @@ class QTimer;
 class QWheelEvent;
 
 // Renders a VNC framebuffer and forwards local input, scaled-to-fit --
-// same shape as RdpDisplayWidget, minus cursor-shape sync (out of scope for
-// the initial VNC implementation; the system cursor is left alone).
+// same shape as RdpDisplayWidget, including remote cursor-shape sync.
 class VncDisplayWidget : public QWidget
 {
     Q_OBJECT
@@ -38,6 +38,15 @@ public:
         return m_scaleToFit;
     }
 
+    // Mirrors RdpDisplayWidget's cursor handling. VNC's Cursor pseudo-
+    // encoding never signals "reset to default" the way RDP's SetDefault
+    // callback does -- it only ever supplies a shape or hides the cursor --
+    // so setCursorDefault() exists for symmetry/future use but VNC sessions
+    // never call it today.
+    void setCursorImage(const QImage& image, const QPoint& hotspot);
+    void setCursorHidden();
+    void setCursorDefault();
+
 signals:
     void keyInput(int key, quint32 nativeScanCode, const QString& text, bool pressed, int modifiers);
     void mouseMoveInput(int x, int y);
@@ -59,10 +68,19 @@ protected:
     bool focusNextPrevChild(bool next) override;
 
 private:
+    enum class CursorMode {
+        Default,
+        Hidden,
+        Custom,
+    };
+
     QImage m_frame;
     QSize m_remoteSize;
     QTimer* m_resizeDebounceTimer;
     bool m_scaleToFit;
+    QImage m_cursorImage;
+    QPoint m_cursorHotspot;
+    CursorMode m_cursorMode;
 
     QRectF renderRect() const;
     QPoint mapToRemote(const QPointF& pos) const;
@@ -70,6 +88,7 @@ private:
     void emitViewportGeometry();
     void scheduleViewportGeometryEmit();
     void applySizeConstraint();
+    void applyCursor();
 };
 
 #endif