[client] input: stop absolute cursor feedback

X11's legacy guest-position synchronization warps the host cursor to
delayed guest updates. With absolute input this feeds old positions back
through cooked motion and pulls the cursor away from window edges.

Skip display-server guest synchronization when the active input is
absolute. Relative input and explicit uncapture alignment are unchanged.

client/src/core.c

@@ -642,6 +642,11 @@ void core_stopFrameThread(void)
 
 void core_handleGuestMouseUpdate(void)
 {
+  /* The local cursor is authoritative with absolute input. Sending delayed
+   * guest positions back to the display server creates a warp feedback loop. */
+  if (lgInput_supports(LG_INPUT_SUPPORT_MOUSE_ABSOLUTE))
+    return;
+
   struct DoublePoint localPos;
   if (!util_guestCurToLocal(&localPos))
   {