RDP: fix resize corruption by proactively resizing the local GDI buffer

update->DesktopResize (the only place gdi_resize() was called) only fires
during a full Deactivation-Reactivation sequence or a GFX ResetGraphics
PDU, neither of which our Display Control channel resize path (SendMonitorLayout,
MS-RDPEDISP) triggers. The client's own display buffer was left stuck at
its initial-connect size for the rest of the session, and FreeRDP's surface-bits
handling silently drops updates outside those stale bounds -- producing
the missing/misplaced taskbar and stale composited-looking content.

sendDisplayResize now calls gdi_resize() itself right after a successful
SendMonitorLayout, rather than waiting on a callback that structurally
never fires for this channel/codec configuration.

Fixes #18.

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

src/rdp_session_backend.cpp

@@ -1933,6 +1933,30 @@ bool RdpSessionBackend::sendDisplayResize(rdp_freerdp* instance, int width, int
             m_lastResizeHeight = height;
             m_lastResizeScale = static_cast<int>(scaleValue);
 
+            // The Display Control channel (MS-RDPEDISP) has no server
+            // acknowledgment PDU, and real hosts apply the new resolution
+            // without a Deactivation-Reactivation sequence — so
+            // update->DesktopResize (which only fires for that sequence, or
+            // for the GFX/Progressive pipeline we don't use) never runs for
+            // a channel-driven resize. Without a matching gdi_resize() call,
+            // gdi->width/height stay at the old size, and FreeRDP's own
+            // surface-bits handling (intersect_rect in gdi.c) then silently
+            // *drops* any update reaching outside those stale bounds —
+            // which is what produced the missing/misplaced taskbar and
+            // stale composited-looking content: this call is the fix, not
+            // just a best-effort nudge.
+            if (instance->context->gdi != nullptr
+                && gdi_resize(instance->context->gdi, static_cast<UINT32>(width),
+                              static_cast<UINT32>(height))) {
+                emit remoteDesktopSizeChanged(width, height);
+            } else if (instance->context->gdi != nullptr) {
+                emit eventLogged(QStringLiteral(
+                    "RDP warning: local resize to %1x%2 failed; display may show stale content "
+                    "until the next full repaint.")
+                                     .arg(width)
+                                     .arg(height));
+            }
+
             // Best-effort nudge: some hosts don't fully repaint their own
             // desktop after a resolution change (observed: taskbar missing
             // until something else forces a redraw). Explicitly asking for