perf: schedule frame after every grab motion for 144Hz smoothness

Without schedule_frame, drag/resize updates sit in the scene graph
until the next natural vsync. At 144Hz this is 7ms max. Scheduling
after each motion ensures the next frame picks up the move/resize.

src/backend/wayland/wl_grab.c

@@ -131,6 +131,10 @@ wl_grab_apply_motion(void)
             }
         }
     }
+
+    /* Ensure the scene renders this frame — at 144 Hz this gives 7ms latency */
+    if (wl_state.output)
+        wlr_output_schedule_frame(wl_state.output);
 }
 
 void