[client] wayland: implement HDR support

client/src/main.h

@@ -154,6 +154,11 @@ struct AppState
   enum MicDefaultState micDefaultState;
 
   int spiceHotX, spiceHotY;
+
+  // Set to true when setHDRImageDescription() returns false, indicating
+  // the display server could not apply the HDR image description.
+  // Checked by the renderer to fall back to software tone-mapping.
+  _Atomic(bool) hdrDescFailed;
 };
 
 struct AppParams