macbook: re-enable touchpad when DWT service stops

Add ExecStopPost to write 0 to bcm5974's inhibited sysfs node,
so the touchpad is always restored even if the script is killed
mid-inhibit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hosts/FredOS-Macbook.nix

@@ -45,6 +45,14 @@
         Type = "simple";
         Restart = "on-failure";
         RestartSec = 3;
+        ExecStopPost = pkgs.writeShellScript "dwt-uninhibit" ''
+          for p in /sys/class/input/event*/device/name; do
+            if grep -q bcm5974 "$p" 2>/dev/null; then
+              echo 0 > "''${p%/name}/inhibited"
+            fi
+          done
+          true
+        '';
         ExecStart = "${pkgs.python3.withPackages (p: [])}/bin/python3 ${pkgs.writeText "macbook-dwt.py" ''
 import glob, os, select, struct, time