[client] display: use trusted nominal cadence

Always track Wayland surface outputs alongside fractional scaling and use
RandR modes for X11 cadence. Remove render-derived feedback so a
throttled client cannot teach the producer to remain throttled.

Release scheduling after nominal output timing remains unavailable.

client/displayservers/X11/x11.h

@@ -76,11 +76,15 @@ struct X11DSState
   bool              jitRender;
   _Atomic(uint64_t) presentMsc, presentUst;
   _Atomic(uint64_t) presentPeriod;
+  _Atomic(uint64_t) nominalPeriod;
   uint32_t          presentSerial;
   Pixmap            presentPixmap;
   XserverRegion     presentRegion;
   LGEvent *         frameEvent;
 
+  bool xrandrSupported;
+  int  xrandrEvent;
+
   LGThread * eventThread;
 
   int xinputOp;