finetune mouse acceleration

hosts/nixos/thinkpad/system.nix

@@ -111,6 +111,13 @@
     accelProfile = "adaptive";
   };
 
+  # TrackPoint configuration (treated as mouse device)
+  services.libinput.mouse = {
+    accelSpeed = "0.0";         # Higher sensitivity for trackpoint (-1.0 to 1.0)
+    accelProfile = "flat";      # No acceleration curve for precise control
+    middleEmulation = false;    # ThinkPad trackpoints have real middle buttons
+  };
+
   # Power management for laptops
   powerManagement = {
     enable = true;